Question 1

A vertical rope is attached to an object that has a mass of 40.0 kg and is at rest.The tension in the rope needed to give the object an upward speed of 3.50 m/s in 0.700 s is
A)592 N
B)390 N
C)200 N
D)980 N
E)720 N

Accepted Answer

To calculate the tension in the rope, we need to consider both the force needed to overcome gravity and the force needed to accelerate the object upwards. The force to overcome gravity (weight) is given by $F_g = mg$, where $m = 40.0 \, \text{kg}$ is the mass of the object and $g = 9.8 \, \text{m/s}^2$ is the acceleration due to gravity. This gives us $F_g = 40.0 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 392 \, \text{N}$.To find the force needed to accelerate the object, we use Newton's second law, $F = ma$, where $a$ is the acceleration. The acceleration can be found using the formula $a = \frac{\Delta v}{\Delta t}$, where $\Delta v = 3.50 \, \text{m/s}$ is the change in velocity and $\Delta t = 0.700 \, \text{s}$ is the time taken. This gives us $a = \frac{3.50 \, \text{m/s}}{0.700 \, \text{s}} = 5.00 \, \text{m/s}^2$. The force needed to accelerate the object is then $F_a = 40.0 \, \text{kg} \times 5.00 \, \text{m/s}^2 = 200 \, \text{N}$.The total tension in the rope is the sum of these two forces: $T = F_g + F_a = 392 \, \text{N} + 200 \, \text{N} = 592 \, \text{N}$.

Question 2

You want to elope by sliding down a nylon rope made by tying stockings together.The rope will withstand a maximum tension of 300 N without breaking.Your mass is 61.2 kg.The magnitude of the smallest acceleration a with which you can slide down the rope is A)9.81 m/s² B)4.91 m/s² C)zero D)2.40 m/s² E)19.6 m/s²

Accepted Answer

The maximum tension the rope can withstand is 300 N, which means the force exerted on the rope by the weight of the person sliding down should not exceed 300 N.

We can find the force exerted on the rope by the following formula:

force = mass x acceleration (F = ma)

In this case, the force is the tension on the rope, which is 300 N. The mass is 61.2 kg. Solving for acceleration, we get:

300 N = 61.2 kg x a

a = 300 N / 61.2 kg

a ≈ 4.91 m/s²

Therefore, the smallest acceleration with which the person can slide down the rope without breaking it is approximately 4.91 m/s², which is choice B.

Question 3

A particle of mass 1.3 kg is sliding down a frictionless slope inclined at 30º to the horizontal.The acceleration of the particle down the slope is A)1.3 m/s² B)9.8 m/s² C)0.5 m/s² D)8.5 m/s² E)4.9 m/s²

Accepted Answer

The acceleration down the slope can be found using the formula:
a = g*sin(θ)
where g is the acceleration due to gravity and θ is the angle of the slope.
Substituting the values, we get:
a = 9.8 m/s² * sin(30º)
a = 4.9 m/s²
Therefore, the correct choice is E)4.9 m/s².

Question 4

A particle has a mass of 6.0 $\times$ 10^-6 kg and a velocity of 800 m/s along the x axis when a force of 14.4 $\times$ 10^-5 N along the y axis acts on the particle at right angles to its velocity.The acceleration of the particle is A)24 m/s² along the x axis. B)zero. C)impossible to determine; forces never act at right angles to velocities. D)24 m/s² along the y axis. E)tangential.

Accepted Answer

The force is acting perpendicular to the velocity, so it will not change the velocity in the x direction. The acceleration will only be in the y direction, and can be found using Newton's second law: F = m*a. So, a = F/m = (14.4*10^-5)/(6.0*10^-6) = 2.4 m/s^2. The direction of this acceleration will be 90 degrees from the direction of the force, which is along the y axis. Therefore, the answer is D.

Question 5

A force of 3.0 N acts on a body along a direction 30º above the horizontal.In addition,there is a gravitational force of 4.0 N downward.The resultant force has a magnitude of
A)7.0 N
B)6.8 N
C)6.1 N
D)3.6 N
E)5.0 N

Accepted Answer

The answer of A force of 3.0 N acts on...

Question 6

Three forces F₁,F₂ and F₃act on an object.If F₁ = 3N i + 5N j + 7N k,F₂ = -5N i - 2N j -2N k,and the object is moving at constant velocity then the vector force F₃ is A)-2N i - 3N j - 5N k B)2N i - 3N j - 5N k C)2N i + 3N j - 5N k D)-8N i - 7N j - 9N k E)8N i + 7 N j +9N k

Accepted Answer

Since the object is moving at constant velocity, the net force acting on it is zero. Therefore, the vector sum of the three forces must be zero. We can find the vector sum as follows: F₃ = - F₁ - F₂ Substituting the given values, we get: F₃ = - 3N i - 5N j - 7N k - 105N i - 102N j -102N k = - 108N i - 7N j - 9N k Therefore, the answer is choice B: 2N i - 3N j + 5N k.

Question 7

Your heart pumps 80 g of blood with each beat.The blood starts from rest and reaches a speed of 0.60 m/s in the aorta.If each beat takes 0.16 s,the average force exerted on the blood is A)3.0 $\times$ 10² N B)0.22 N C)0.16 N D)0.30 N E)0.98 N

Accepted Answer

The mass of blood pumped with each beat is 80 g = 0.08 kg. 
The final velocity of blood is 0.60 m/s. 
The time taken for blood to reach this velocity is equal to the time for one beat, which is 0.16 s.

Using the equation: 
average force = (mass x final velocity)/time

we get: 
average force = (0.08 kg x 0.60 m/s)/0.16 s 
average force = 0.30 N

Therefore, the best choice is D) 0.30 N.

Question 8

A bell hangs from a blue rope.A red rope attached to the side of the bell is pulled in the horizontal direction.This causes the blue rope to make an angle less than 90º with the vertical.Which of the following statements is true?
A)The red rope is under greater tension than the blue rope.
B)The red rope is under the same tension as the blue rope.
C)The blue rope is under greater tension than the red rope.
D)The tensions cannot be compared unless the mass of the bell is known.
E)The tensions cannot be compared unless the angle that the blue rope makes with the vertical is known.

Accepted Answer

The tension in the blue rope is greater than the tension in the red rope. This is because the blue rope is supporting the weight of the bell in addition to the tension due to the horizontal force applied by the red rope. The angle less than 90º indicates that the tension in the blue rope has a vertical component, which means more force is needed from the blue rope to keep the bell from falling.

Question 9

Three forces,  ,  ,and  ,act on a mass of 4.2 kg.The forces are  The direction of the net acceleration
A)cannot be determined because the acceleration is zero.
B)is 60º north of east.
C)is 70º north of east.
D)is 51º north of east.
E)is 44º north of east.

Accepted Answer

The answer of Three forces,  ,  ,and ...

Question 10

A lamp of mass m hangs from a spring scale that is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read while the elevator descends toward the ground floor at a constant speed?
A)more than mg
B)less than mg
C)mg
D)zero
E)This cannot be answered without knowing how fast the elevator is descending.

Accepted Answer

When the elevator is stopped, the reading on the scale is simply the weight of the lamp, which is mg. The scale measures the force exerted on it by the lamp due to gravity. When the elevator descends at a constant speed, the lamp is still stationary relative to the elevator, and so the reading on the scale will not change. The force exerted by the lamp due to gravity is still mg, so the scale will continue to read mg. The speed of the elevator is not relevant in this case, as long as it is descending at a constant speed.

Question 11

A lamp of mass m hangs from a spring scale which is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read as the elevator slows down to stop at the ground floor?
A)more than mg
B)less than mg
C)mg
D)zero
E)One cannot tell without knowing how fast the elevator is stopping.

Accepted Answer

When the elevator slows down (decelerates) while moving downwards, the effective acceleration due to gravity increases, causing the scale to read a value greater than mg.

Question 12

A box sits on an inclined plane without sliding.As the angle of inclination increases,the normal force
A)increases.
B)decreases.
C)does not change.
D)is directed upward.
E)is directed in the direction of the gravitational force.

Accepted Answer

As the angle of inclination increases, the component of gravitational force acting on the box parallel to the inclined plane increases. This results in a decrease in the normal force acting on the box perpendicular to the inclined plane, leading to a decrease in the total force opposing the gravitational force. Therefore, choice B is correct as the normal force decreases.

Question 13

A boy holds a bird in his hand.The reaction force to the normal force exerted on the bird by the boy's hand is the force of:
A)the Earth on the bird.
B)the bird on the Earth.
C)the hand on the bird.
D)the bird on the hand.
E)the Earth on the hand.

Accepted Answer

According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction. In this case, the normal force exerted on the bird by the boy's hand is the action force, and the reaction force is the force exerted on the hand by the bird. Therefore, the correct choice is D, the bird on the hand.

Question 14

Three forces, , ,and ,act on a mass of 4.2 kg.The forces are The magnitude of the net acceleration of the mass is A)2.9 m/s² B)5.3 m/s² C)1.4 m/s² D)0.0 m/s² E)18 m/s²

Accepted Answer

The answer of Three forces,  ,  ,and ...

Question 15

A net force is exerted on an object toward the north.The object
A)is moving toward the north.
B)is moving toward the east.
C)is moving toward the west.
D)is moving toward the south.
E)may be moving in any direction.

Accepted Answer

A net force exerted toward the north does not necessarily determine the direction of motion of the object. The object may be stationary or already in motion, and the direction of its original motion or other forces acting on it may affect its resulting direction of motion.

Question 16

An 80-kg man on ice skates pushes a 40-kg boy,also on skates,with a force of 100 N.The force exerted by the boy on the man is
A)200 N
B)100 N
C)50 N
D)40 N
E)zero unless the boy pushes back

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, if the man exerts a force of 100 N on the boy, the boy exerts a force of 100 N on the man in the opposite direction.

Question 17

A lamp of mass m hangs from a spring scale that is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read as the elevator slows down to stop at the forty-fifth floor?
A)more than mg
B)less than mg
C)mg
D)zero
E)One cannot tell without knowing how fast the elevator is stopping.

Accepted Answer

The scale will read the weight of the lamp, which is mg, regardless of whether the elevator is moving up, down, or is stationary. The slowing down of the elevator does not affect the reading of the scale.

Question 18

A boy sits in a tire that is attached to a rope that passes over a pulley fastened to the ceiling and then passes back down to the boy's hands.The weight of the boy plus the tire is W.The force with which the boy must pull on the free end of the rope to support his weight in the tire is
A)(1/2)W
B)W
C)2W
D)(2/3)W
E)(3/2)W

Accepted Answer

When the boy pulls on the rope, he creates a tension that is equal throughout the rope. Since there are two segments of the rope supporting his weight (one segment from the pulley to his hands, and the other from the pulley to the tire), the force he needs to apply is half his weight, or (1/2)W, to balance the forces.

Question 19

A man riding in an elevator has an apparent weight greater than his actual weight.Which one of the following statements could be true?
A)The elevator moves upward with constant speed.
B)The elevator moves downward with constant speed.
C)The elevator moves upward with decreasing speed.
D)The elevator moves downward with decreasing speed.
E)The elevator moves downward with increasing speed.

Accepted Answer

The answer of A man riding in an elevator has...

Question 20

The word "normal," as it applies to forces,means
A)usual.
B)mean.
C)average.
D)perpendicular.
E)straight up,in the direction opposite to the force of gravity.

Accepted Answer

In physics, the term "normal force" refers to the force that acts perpendicular to the surface that an object is in contact with. It is not related to the common usage of "normal" meaning usual, mean, average, or any specific direction like straight up.

Quiz 4: Newtons Laws

A vertical rope is attached to an object that has a mass of 40.0 kg and is at rest.The tension in the rope needed to give the object an upward speed of 3.50 m/s in 0.700 s is

You want to elope by sliding down a nylon rope made by tying stockings together.The rope will withstand a maximum tension of 300 N without breaking.Your mass is 61.2 kg.The magnitude of the smallest acceleration a with which you can slide down the rope is

A particle of mass 1.3 kg is sliding down a frictionless slope inclined at 30º to the horizontal.The acceleration of the particle down the slope is

A particle has a mass of 6.0 ×\times× 10-6 kg and a velocity of 800 m/s along the x axis when a force of 14.4 ×\times× 10-5 N along the y axis acts on the particle at right angles to its velocity.The acceleration of the particle is

A force of 3.0 N acts on a body along a direction 30º above the horizontal.In addition,there is a gravitational force of 4.0 N downward.The resultant force has a magnitude of

Three forces F1,F2 and F3 act on an object.If F1 = 3N i + 5N j + 7N k,F2 = -5N i - 2N j -2N k,and the object is moving at constant velocity then the vector force F3 is

Your heart pumps 80 g of blood with each beat.The blood starts from rest and reaches a speed of 0.60 m/s in the aorta.If each beat takes 0.16 s,the average force exerted on the blood is

A bell hangs from a blue rope.A red rope attached to the side of the bell is pulled in the horizontal direction.This causes the blue rope to make an angle less than 90º with the vertical.Which of the following statements is true?

Three forces, , ,and ,act on a mass of 4.2 kg.The forces are The direction of the net acceleration

A lamp of mass m hangs from a spring scale that is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read while the elevator descends toward the ground floor at a constant speed?

A lamp of mass m hangs from a spring scale which is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read as the elevator slows down to stop at the ground floor?

A box sits on an inclined plane without sliding.As the angle of inclination increases,the normal force

A boy holds a bird in his hand.The reaction force to the normal force exerted on the bird by the boy's hand is the force of:

Three forces, , ,and ,act on a mass of 4.2 kg.The forces are The magnitude of the net acceleration of the mass is

A net force is exerted on an object toward the north.The object

An 80-kg man on ice skates pushes a 40-kg boy,also on skates,with a force of 100 N.The force exerted by the boy on the man is

A lamp of mass m hangs from a spring scale that is attached to the ceiling of an elevator.When the elevator is stopped at the fortieth floor,the scale reads mg.What does it read as the elevator slows down to stop at the forty-fifth floor?

A boy sits in a tire that is attached to a rope that passes over a pulley fastened to the ceiling and then passes back down to the boy's hands.The weight of the boy plus the tire is W.The force with which the boy must pull on the free end of the rope to support his weight in the tire is

A man riding in an elevator has an apparent weight greater than his actual weight.Which one of the following statements could be true?

The word "normal," as it applies to forces,means

A particle has a mass of 6.0 $\times$ 10^-6 kg and a velocity of 800 m/s along the x axis when a force of 14.4 $\times$ 10^-5 N along the y axis acts on the particle at right angles to its velocity.The acceleration of the particle is

Three forces F₁,F₂ and F₃act on an object.If F₁ = 3N i + 5N j + 7N k,F₂ = -5N i - 2N j -2N k,and the object is moving at constant velocity then the vector force F₃ is