Deck 4: Force and Newtons Laws of Motion

Question 1

Three objects experience interactions. Object $\mathrm{A}$ has mass, object $\mathrm{B}$ has electrical charge, and object $\mathrm{C}$ has both mass and electrical charge. Which of the following statements is true?

A) Object A and object B experience an electrical interaction.
B) Object $\mathrm{A}$ and object $\mathrm{C}$ experience a gravitational interaction.
C) Object $\mathrm{A}$ and object $\mathrm{B}$ experience a gravitational interaction.
D) Object $\mathrm{A}$ and object $\mathrm{C}$ experience an electrical interaction.

Answer 1

Object $\mathrm{A}$ and object $\mathrm{C}$ experience a gravitational interaction.

Question 2

If an object of mass $20 \mathrm{~kg}$ on Earth is sent to the Moon, it will have a mass of

A) $0.0 \mathrm{~kg}$ .
B) $20 \mathrm{~kg}$ .
C) $4.0 \mathrm{~kg}$ .
D) $10 \mathrm{~kg}$ .

Answer 2

$20 \mathrm{~kg}$ .

Question 3

A freight train consists of an engine and several identical cars on a straight, level track. Which of the following statements is true?

A) If the train is moving at constant speed, the engine must be pulling with a force greater than the train's weight.
B) If the train is moving at constant speed, the engine's pull on the first car must exceed that car's backward pull on the engine.
C) If the train is moving at constant speed, the engine's pull must be equal to the force of friction.
D) If the train is coasting, its inertia makes it slow down and eventually stop.

Answer 3

If the train is moving at constant speed, the engine's pull must be equal to the force of friction.

Question 4

In the figure an airport luggage carrying train with a tractor $T$ is pulling three luggage carts $M_{1}, M_{2}$ , and $M_{3}$ , with constant velocity of $4.5 \mathrm{~m} / \mathrm{s}$ . Unfortunately, the wheels on the carts have locked up and are sliding rather than rolling. If $T=300.0 \mathrm{~kg}, M_{1}=200.0 \mathrm{~kg}, M_{2}=100.0 \mathrm{~kg}$ , and $M_{3}=100.0 \mathrm{~kg}$ , and the coefficient of kinetic friction for each is 0.4000 , what is the force in the connection between the tractor $\mathrm{T}$ and cart $\mathrm{M}_{1}$ ? Use $\mathrm{g}=9.8 \mathrm{~m} / \mathrm{s}$ .

A) $1862 \mathrm{~N}$
B) $1568 \mathrm{~N}$
C) $2941 \mathrm{~N}$
D) $2744 \mathrm{~N}$
E) $2439 \mathrm{~N}$

Question 5

In the figure, an airport luggage carrying train with a tractor $T$ is pulling three luggage carts, $M_{1}, M_{2}$ , and $M_{3}$ , with constant velocity of $4.5 \mathrm{~m} / \mathrm{s}$ . If $T=300 \mathrm{~kg}, M_{1}=200 \mathrm{~kg}, M_{2}=100 \mathrm{~kg}$ , and $M_{3}=100 \mathrm{~kg}$ (there is no friction), then the force in the connection between the tractor $\mathrm{T}$ and cart $\mathrm{M}_{1}$ is

A) $280 \mathrm{~N}$ .
B) $560 \mathrm{~N}$ .
C) $980 \mathrm{~N}$ .
D) $0.00 \mathrm{~N}$ .
E) $140 \mathrm{~N}$ .

Question 6

A large massive rock is in contact with the Earth. Draw a force diagram for the rock and the Earth. Which of the following statements is true?

A) The gravitational force on the rock due to the Earth and the gravitational force on the Earth due to the rock are interaction partners.
B) The gravitational force on the Earth due to the rock and the contact force on the Earth due to the rock are interaction partners.
C) The gravitational force on the rock due to the Earth and the contact force on the Earth due to the rock are interaction partners.
D) The contact force on the Earth due to the rock and the gravitational force on the Earth due to the rock are interaction partners.

Question 7

What is the gravitational field strength on the surface of the Earth? $\left(\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right.$ , the mass of the Earth is $5.98 \times 10^{24} \mathrm{~kg}$ , and the radius of the Earth is $6.38 \times 10^{6} \mathrm{~m}$ .)

A) $10.1 \mathrm{~N} / \mathrm{kg}$ .
B) $6.20 \mathrm{~N} / \mathrm{kg}$ .
C) $20.3 \mathrm{~N} / \mathrm{kg}$ .
D) $9.80 \mathrm{~N} / \mathrm{kg}$ .
E) $3.40 \mathrm{~N} / \mathrm{kg}$ .

Question 8

What is the gravitational field strength at the location of a satellite that is orbiting the Earth at an altitude of $5,000 \mathrm{~km} ?\left(\mathrm{G}=6.67 \times 10^{-11} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right.$ , the mass of the Earth is $5.98 \times 10^{24} \mathrm{~kg}$ , and the radius of the Earth is $6.38 \times 106 \mathrm{~m}$ .)

A) $8.43 \mathrm{~N} / \mathrm{kg}$ .
B) $9.55 \mathrm{~N} / \mathrm{kg}$ .
C) $5.28 \mathrm{~N} / \mathrm{kg}$
D) $6.33 \mathrm{~N} / \mathrm{kg}$ .
E) $3.08 \mathrm{~N} / \mathrm{kg}$ .

Question 9

The gravitational field at the Moon due to the Earth is approximately ( $\mathrm{G}=6.67 \times 10^{-11} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}$ , the mass of the Earth is $5.98 \times 10^{24} \mathrm{~kg}$ , and the distance to the Moon is $3.85 \times 10^{8} \mathrm{~m}$ )

A) $7.30 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Earth.
B) $2.69 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ away from the Earth.
C) $7.30 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ away from the Earth.
D) $5.00 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Earth.
E) $2.69 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Earth.

Question 10

The gravitational field at the Earth due to the Moon is about ( $\mathrm{G}=6.67 \times 10^{-11} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}$ , the mass of the Moon is $7.35 \times 10^{22} \mathrm{~kg}$ , and the distance to the Moon is $3.85 \times 10^{8} \mathrm{~m}$ )

A) $7.50 \times 10-5 \mathrm{~N} / \mathrm{kg}$ away from the Moon.
B) $2.90 \times 10-5 \mathrm{~N} / \mathrm{kg}$ away from the Moon.
C) $4.01 \times 10^{-5} \mathrm{~N} / \mathrm{kg}$ toward the Moon.
D) $3.31 \times 10^{-5} \mathrm{~N} / \mathrm{kg}$ away from the Moon.
E) $3.31 \times 10^{-5} \mathrm{~N} / \mathrm{kg}$ toward the Moon.

Question 11

The Moon (mass $7.35 \times 10^{22} \mathrm{~kg}$ ) orbits the Earth (mass $5.98 \times 10^{24} \mathrm{~kg}$ ) at a distance of $3.85 \times 10^{8}$ meters. Meanwhile, the Earth orbits the Sun (mass $1.99 \times 1030 \mathrm{~kg}$ ) at a distance of $1.50 \times 1011$ meters. When the Moon is directly between the Earth and the Sun, what is the gravitational field at the location of the Moon due to the Earth and the Sun combined? $\left(\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right)$

A) $3.21 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Sun
B) $3.21 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Earth
C) $5.93 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Sun
D) $2.69 \times 10-3 \mathrm{~N} / \mathrm{kg}$ toward the Earth
E) $5.93 \times 10^{-3} \mathrm{~N} / \mathrm{kg}$ toward the Earth

Question 12

The Moon (mass $7.35 \times 10^{22} \mathrm{~kg}$ ) is orbiting about the Earth (mass $5.98 \times 10^{24} \mathrm{~kg}$ ) at a radius of $3.85 \times 10^{8}$ meters. The magnitude of the force of gravity on the Moon due to the Earth is $\left(G=6.67 \times 10^{-11} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right)$

A) $4.10 \times 1012 \mathrm{~N}$ .
B) $1.98 \times 1020 \mathrm{~N}$ .
C) $9.20 \times 1030 \mathrm{~N}$ .
D) $6.70 \times 1024 \mathrm{~N}$ .
E) $3.20 \times 10^{28} \mathrm{~N}$ .

Question 13

An object with a mass of $200.0 \mathrm{~kg}$ is $500.0 \mathrm{~km}$ above the surface of the Earth. The magnitude of the force of gravity on the $200.0 \mathrm{~kg}$ mass is $\left(\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right.$ , the radius of the Earth is $6.38 \times 10^{6} \mathrm{~m}$ , and the mass of the Earth is $5.98 \times 1024 \mathrm{~kg}$ )

A) $1.05 \times 10^{3} \mathrm{~N}$ .
B) $2.02 \times 10^{3} \mathrm{~N}$ .
C) $1.42 \times 10^{3} \mathrm{~N}$ .
D) $1.69 \times 10^{3} \mathrm{~N}$ .
E) $1.28 \times 10^{3} \mathrm{~N}$ .

Question 14

What is the gravitational force between two $5.00 \mathrm{~kg}$ masses that are $10.0 \mathrm{~cm}$ apart from center to center? (G $=6.67 \times 10^{-11} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}$ )

A) $1.67 \times 10-8 \mathrm{~N}$
B) $1.67 \times 10^{-4} \mathrm{~N}$
C) $1.62 \times 10^{-6} \mathrm{~N}$
D) $1.62 \times 10^{-5} \mathrm{~N}$
E) $1.67 \times 10^{-7} \mathrm{~N}$

Question 15

What is the gravitational force between two nuclei, each of mass $3.20 \times 10^{-27} \mathrm{~kg}$ , which are separated by a distance of $1.06 \times 10-10 \mathrm{~m} ?\left(\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}\right)$

A) $6.08 \times 10^{-44} \mathrm{~N}$
B) $6.08 \times 10-43 \mathrm{~N}$
C) $6.08 \times 10^{-45} \mathrm{~N}$
D) $6.08 \times 10^{-42} \mathrm{~N}$

Question 16

The weight of a $1.00 \mathrm{~kg}$ object on the surface of the Moon is ( $\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m} 2 / \mathrm{kg}^{2}$ , the radius of the Moon is $1.74 \times 10^{6} \mathrm{~m}$ , and the mass of the Moon is $7.35 \times 10^{22} \mathrm{~kg}$ )

A) $7.59 \mathrm{~N}$ .
B) $1.62 \mathrm{~N}$ .
C) $0.548 \mathrm{~N}$ .
D) $0.981 \mathrm{~N}$ .
E) $9.80 \mathrm{~N}$ .

Question 17

The Moon (mass $7.35 \times 1022 \mathrm{~kg}$ ) orbits the Earth (mass $5.98 \times 10^{24} \mathrm{~kg}$ ) at a distance of $3.85 \times 10^{8}$ meters. Meanwhile, the Earth orbits the Sun (mass $1.99 \times 1030 \mathrm{~kg}$ ) at a distance of $1.50 \times 1011$ meters. When the Moon is directly between the Earth and the Sun, what is the gravitational force on the Moon due to the Earth and the Sun combined? ( $\mathrm{G}=6.67 \times 10-11 \mathrm{~N} \mathrm{~m}^{2} / \mathrm{kg}^{2}$ )

A) $4.36 \times 1020 \mathrm{~N}$ toward the Earth
B) $2.36 \times 10^{20} \mathrm{~N}$ toward the Sun
C) $2.38 \times 10^{20} \mathrm{~N}$ toward the Earth
D) $4.36 \times 1020 \mathrm{~N}$ toward the Sun
E) $1.98 \times 10^{20} \mathrm{~N}$ toward the Earth

Question 18

A boy with a mass of $55 \mathrm{~kg}$ walks into a room and sees a girl $8.0 \mathrm{~m}$ in front of him who has a mass of $40 \mathrm{~kg}$ . What is his gravitational attraction to her?

A) $2.0 \times 10^{8} \mathrm{~N}$
B) $2.1 \times 10^{9} \mathrm{~N}$
C) $2.3 \times 10^{-9} \mathrm{~N}$
D) $2.4 \times 10-8 \mathrm{~N}$
E) $2.2 \times 10-11 \mathrm{~N}$

Question 19

A mass sits at rest on top of a table. Which two forces that are not action-reaction partners are equal and opposite?

A) the force of gravity on the mass due to the Earth and the contact force on the mass due to the table
B) the contact force on the mass due to the table and the force of gravity on the Earth due to the mass
C) the contact force on the mass due to the table and the contact force on the table due to the mass
D) the force of gravity on the mass due to the Earth and the contact force on the table due to the mass
E) the force of gravity on the mass due to the Earth and the force of gravity on the Earth due to the mass

Question 20

Within a given system, the internal forces

A) determine the motion of the system.
B) are always balanced by the external forces.
C) all add to zero.
D) are measured with a gravimeter.
E) are only determined by subtracting the external forces from the net force on the system.

Question 21

A rope is connected to a spring scale on the left and exerts a force $T_{1}$ . Another rope is connected to the scale on the right and exerts a force $T_{2}$ . The scale shows a reading of $T_{s}=120 \mathrm{~N}$ . The values of $T_{1}$ and $T_{2}$ are

A) $\mathrm{T}_{1}=80 \mathrm{~N}$ , and $\mathrm{T}_{2}=120 \mathrm{~N}$ .
B) $\mathrm{T}_{1}=80 \mathrm{~N}$ , and $\mathrm{T}_{2}=80 \mathrm{~N}$ .
C) $\mathrm{T}_{1}=240 \mathrm{~N}$ , and $\mathrm{T}_{2}=240 \mathrm{~N}$ .
D) $\mathrm{T}_{1}=120 \mathrm{~N}$ , and $\mathrm{T}_{2}=120 \mathrm{~N}$ .

Question 22

A box rests on a frictionless countertop. A boy pushes horizontally to the right on the box, and a girl pushes on it to the left, yet it remains stationary. Which of the following statements is false?

A) We know the force of the boy on the box is equal in magnitude to the force of the girl on the box, because the box is in equilibrium.
B) We know the weight and normal force are equal in magnitude because the box is in equilibrium.
C) We know the weight and normal force are equal in magnitude because of Newton's third law.
D) We know the force of the boy on the box is equal in magnitude to the force of the box on the boy, because of Newton's third law.

Question 23

A tractor $\mathrm{T}$ is pulling a trailer $\mathrm{M}$ with a constant velocity. If the velocity is $20 \mathrm{~m} / \mathrm{s}$ and $\mathrm{M}=200 \mathrm{~kg}$ and $\mathrm{T}=$ $500 \mathrm{~kg}$ , then the force on the trailer due to the tractor is (assume there is no friction or air resistance)

A) $600 \mathrm{~N}$ forward.
B) $450 \mathrm{~N}$ backward.
C) 0 .
D) $35 \mathrm{~N}$ forward.
E) $200 \mathrm{~N}$ backward.

Question 24

A tractor $\mathrm{T}$ is pulling a trailer $\mathrm{M}$ with a constant acceleration. If the forward acceleration is $1.5 \mathrm{~m} / \mathrm{s}^{2}$ and $\mathrm{M}=$ $400 \mathrm{~kg}$ and $\mathrm{T}=500 \mathrm{~kg}$ , then the force on the tractor due to the trailer is (ignore air resistance)

A) $35 \mathrm{~N}$ forward.
B) $600 \mathrm{~N}$ backward.
C) $450 \mathrm{~N}$ backward.
D) 0 .
E) $200 \mathrm{~N}$ forward.

Question 25

A tractor $T$ is pulling a trailer $M$ with a constant acceleration. If the forward acceleration is $0.50 \mathrm{~m} / \mathrm{s}^{2}$ and $M$ $=400 \mathrm{~kg}$ and $\mathrm{T}=500 \mathrm{~kg}$ , then the horizontal force on the tractor due to the ground is (ignore air resistance)

A) $450 \mathrm{~N}$ backward.
B) $250 \mathrm{~N}$ forward.
C) $200 \mathrm{~N}$ forward.
D) $250 \mathrm{~N}$ backward.
E) $450 \mathrm{~N}$ forward.

Question 26

A tractor $T$ is pulling two trailers, $M_{1}$ and $M_{2}$ , with a constant acceleration. $T$ has a mass of $200 \mathrm{~kg}, M_{1}$ has a mass of $100 \mathrm{~kg}$ , and $M_{2}$ has a mass of $150 \mathrm{~kg}$ . If the forward acceleration is $0.60 \mathrm{~m} / \mathrm{s}^{2}$ , then the horizontal force on the tractor due to the ground is (ignore air resistance)

A) $90 \mathrm{~N}$ forward.
B) $150 \mathrm{~N}$ forward.
C) $270 \mathrm{~N}$ forward.
D) $150 \mathrm{~N}$ backward.
E) $270 \mathrm{~N}$ backward.

Question 27

A tractor $T$ is pulling two trailers, $M_{1}$ and $M_{2}$ , with a constant acceleration. Thas a mass of $200 \mathrm{~kg}, M_{1}$ has a mass of $100 \mathrm{~kg}$ , and $\mathrm{M}_{2}$ has a mass of $150 \mathrm{~kg}$ . If the forward acceleration is $0.60 \mathrm{~m} / \mathrm{s}^{2}$ , and air resistance is negligible, then the horizontal force on the tractor due to the attachment to $\mathrm{M}_{1}$ is

A) $270 \mathrm{~N}$ backward.
B) $150 \mathrm{~N}$ forward.
C) $150 \mathrm{~N}$ backward.
D) $270 \mathrm{~N}$ forward.
E) $90 \mathrm{~N}$ forward.

Question 28

A tractor $T$ is pulling two trailers, $M_{1}$ and $M_{2}$ , with a constant acceleration. Thas a mass of $200 \mathrm{~kg}, M_{1}$ has a mass of $100 \mathrm{~kg}$ , and $\mathrm{M}_{2}$ has a mass of $150 \mathrm{~kg}$ . If the forward acceleration is $0.60 \mathrm{~m} / \mathrm{s}^{2}$ , and air resistance is negligible, then the horizontal force on $\mathrm{M}_{2}$ due to the attachment to $\mathrm{M}_{1}$ is

A) $270 \mathrm{~N}$ forward.
B) $270 \mathrm{~N}$ backward.
C) $90 \mathrm{~N}$ forward.
D) $150 \mathrm{~N}$ forward.
E) $150 \mathrm{~N}$ backward.

Question 29

A tractor of mass $M_{1}=2,000 \mathrm{~kg}$ is pulling a trailer of mass $M_{2}=5,000 \mathrm{~kg}$ . If the tractor-trailer is accelerated at $2.0 \mathrm{~m} / \mathrm{s}^{2}$ , and air resistance is negligible, then the tension in the trailer hitch that connects the trailer to the tractor is

A) $8,000 \mathrm{~N}$ .
B) $6,000 \mathrm{~N}$ .
C) $11,000 \mathrm{~N}$ .
D) $10,000 \mathrm{~N}$ .
E) $9,000 \mathrm{~N}$ .

Question 30

A tractor of mass $M_{1}=2,000 \mathrm{~kg}$ is pulling a trailer of mass $M_{2}=5,000 \mathrm{~kg}$ . If the tractor-trailer is accelerated at $2.0 \mathrm{~m} / \mathrm{s}^{2}$ , and air resistance is negligible, then the magnitude of the force the tractor applies to the road is

A) $12,000 \mathrm{~N}$
B) $14,000 \mathrm{~N}$
C) $6,000 \mathrm{~N}$ .
D) $8,000 \mathrm{~N}$ .
E) $10,000 \mathrm{~N}$

Question 31

In the figure, an airport luggage-carrying train with a tractor $T$ is pulling three luggage carts, $M_{1}, M_{2}$ , and $M_{3}$ with an acceleration of $1.2 \mathrm{~m} / \mathrm{s}^{2}$ . If $\mathrm{T}=300 \mathrm{~kg}, \mathrm{M}_{1}=200 \mathrm{~kg}, \mathrm{M}_{2}=100 \mathrm{~kg}$ , and $\mathrm{M}_{3}=100 \mathrm{~kg}$ , and air resistance is negligible, then the tension in the connection between cart $\mathrm{M}_{2}$ and cart $\mathrm{M}_{1}$ is

A) $480 \mathrm{~N}$ .
B) $840 \mathrm{~N}$ .
C) $240 \mathrm{~N}$ .
D) $0 \mathrm{~N}$ .
E) $120 \mathrm{~N}$ .

Question 32

In the figure, an airport luggage-carrying train with a tractor $T$ is pulling three luggage carts, $M_{1}, M_{2}$ , and $M_{3}$ with an acceleration of $1.0 \mathrm{~m} / \mathrm{s}^{2}$ . If $\mathrm{T}=300 \mathrm{~kg}, \mathrm{M}_{1}=200 \mathrm{~kg}, \mathrm{M}_{2}=100 \mathrm{~kg}$ , and $\mathrm{M}_{3}=100 \mathrm{~kg}$ , and air resistance is negligible, then the tension in the connection between cart $\mathrm{M}_{2}$ and cart $\mathrm{M}_{3}$ is

A) $200 \mathrm{~N}$
B) $700 \mathrm{~N}$ .
C) $100 \mathrm{~N}$ .
D) $400 \mathrm{~N}$ .
E) $0 \mathrm{~N}$ .

Question 33

Two masses are suspended by a cord that passes over a pulley with negligible mass. The cord also has negligible mass. One of the masses, $\mathrm{m}_{1}$ , has a mass of $5.0 \mathrm{~kg}$ and the other mass, $\mathrm{m}_{2}$ , has a mass of $3.0 \mathrm{~kg}$ . The acceleration of $\mathrm{m}_{1}$ is

A) $2.5 \mathrm{~m} / \mathrm{s}^{2}$ upward.
B) $2.5 \mathrm{~m} / \mathrm{s}^{2}$ downward.
C) $3.3 \mathrm{~m} / \mathrm{s}^{2}$ upward.
D) $3.3 \mathrm{~m} / \mathrm{s}^{2}$ downward.
E) $1.1 \mathrm{~m} / \mathrm{s}^{2}$ upward.

Question 34

Two masses are suspended by a cord that passes over a pulley with negligible mass. The cord also has negligible mass. One of the masses, $m_{1}$ , has a mass of $7.0 \mathrm{~kg}$ and the other mass, $m_{2}$ , has a mass of $3.0 \mathrm{~kg}$ . The pulley turns on a shaft through the center of the pulley, which supports the pulley and all the masses. The vertical force of the shaft on the pulley is

A) $49 \mathrm{~N}$ downward.
B) $98 \mathrm{~N}$ upward.
C) $82 \mathrm{~N}$ upward.
D) $82 \mathrm{~N}$ downward.
E) $49 \mathrm{~N}$ upward.

Question 35

An $80.0 \mathrm{~kg}$ person is riding in an elevator that is accelerating at $2.40 \mathrm{~m} / \mathrm{s}^{2}$ downward. The apparent weight of the $80.0 \mathrm{~kg}$ person measured on a scale in the elevator is

A) $855 \mathrm{~N}$ .
B) $592 \mathrm{~N}$ .
C) $784 \mathrm{~N}$ .
D) $976 \mathrm{~N}$ .
E) $639 \mathrm{~N}$ .

Question 36

A $78 \mathrm{~kg}$ object is travelling due north at $15.2 \mathrm{~m} / \mathrm{s}$ when it begins to experience a constant net force of 1.72 $\mathrm{kN}$ toward the south. What will its velocity be $0.75 \mathrm{~s}$ later?

A) $1.3 \mathrm{~m} / \mathrm{s}$ , north.
B) $18.8 \mathrm{~m} / \mathrm{s}$ , north.
C) $18.8 \mathrm{~m} / \mathrm{s}$ , south
D) $16.5 \mathrm{~m} / \mathrm{s}$ , north
E) $1.3 \mathrm{~m} / \mathrm{s}$ , south.
F) $16.5 \mathrm{~m} / \mathrm{s}$ , south

Question 37

An object travels $7.5 \mathrm{~m} / \mathrm{s}$ toward the west. Under the influence of a constant net force of $5.2 \mathrm{kN}$ , after $4.3 \mathrm{~s}$ , it is travelling $2.5 \mathrm{~m} / \mathrm{s}$ toward the east. What is its mass?

A) $2200 \mathrm{~kg}$
B) $4500 \mathrm{~kg}$
C) $12000 \mathrm{~kg}$
D) $6000 \mathrm{~kg}$

Question 38

Two masses are connected by a string which passes over a pulley with negligible mass and friction. One mass hangs vertically and one mass slides on a 30.0 degree incline. The inclined surface has a coefficient of kinetic friction of 0.200 . The vertically hanging mass is $6.00 \mathrm{~kg}$ and the mass on the incline is $4.00 \mathrm{~kg}$ . The magnitude of the acceleration of the $4.00 \mathrm{~kg}$ mass is (the initial velocity of the $4.00 \mathrm{~kg}$ mass is down the incline)

A) $1.53 \mathrm{~m} / \mathrm{s}^{2}$ .
B) $7.16 \mathrm{~m} / \mathrm{s}^{2}$ .
C) $5.84 \mathrm{~m} / \mathrm{s}^{2}$ .
D) $0.00 \mathrm{~m} / \mathrm{s}^{2}$ .
E) $2.98 \mathrm{~m} / \mathrm{s}^{2}$ .

Question 39

Two masses are connected by a string which passes over a pulley with negligible mass and friction. One mass hangs vertically and one mass slides on a 30.0 degree incline. The inclined surface has a coefficient of kinetic friction of 0.200 . The vertically hanging mass is $4.00 \mathrm{~kg}$ and the mass on the incline is $6.00 \mathrm{~kg}$ . The magnitude of the acceleration of the $4.00 \mathrm{~kg}$ mass is (the initial velocity of the $6.00 \mathrm{~kg}$ mass is down the incline)

A) $2.98 \mathrm{~m} / \mathrm{s}^{2}$ .
B) $3.90 \mathrm{~m} / \mathrm{s}^{2}$ .
C) $5.84 \mathrm{~m} / \mathrm{s}^{2}$ .
D) $1.53 \mathrm{~m} / \mathrm{s}^{2}$ .
E) $7.16 \mathrm{~m} / \mathrm{s}^{2}$ .

Question 40

Two masses are connected by a string which passes over a pulley with negligible mass and friction. One mass hangs vertically and one mass slides on a horizontal surface. The horizontal surface has a coefficient of kinetic friction of 0.200 . The vertically hanging mass is $3.00 \mathrm{~kg}$ and the mass on the horizontal surface is $3.00 \mathrm{~kg}$ . The magnitude of the acceleration of the vertically hanging mass is (the initial velocity of the horizontal mass is to the right)

A) $2.00 \mathrm{~m} / \mathrm{s}^{2}$ .
B) $4.02 \mathrm{~m} / \mathrm{s}^{2}$ .
C) $7.16 \mathrm{~m} / \mathrm{s}^{2}$ .
D) $5.88 \mathrm{~m} / \mathrm{s}^{2}$ .
E) $3.53 \mathrm{~m} / \mathrm{s}^{2}$ .