Question 1

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the Earth is:

Accepted Answer

The force of the block on the Earth is equal to its weight, which is calculated using the formula $F = mg$, where $m = 5 \, \text{kg}$ and $g = 9.8 \, \text{m/s}^2$. This gives $F = 5 \times 9.8 = 49 \, \text{N}$. According to Newton's third law, this force is exerted equally and oppositely, so the force of the block on the Earth is 49 N, up.

Question 2

You stand on a spring scale on the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

Accepted Answer

The answer of You stand on a spring scale on...

Question 3

A short 10-g string is used to pull a 50-g toy across a frictionless horizontal surface. If a 3.0 * 10^-²-N force is applied horizontally to the free end, the force of the string on the toy, at the other end, is:

Accepted Answer

The force applied to the system (string + toy) is 3.0 x 10^-2 N. The total mass of the system is 60 g (10 g string + 50 g toy), which is 0.06 kg. The acceleration of the system is F/m = (3.0 x 10^-2 N) / 0.06 kg = 0.5 m/s². The force on the toy is its mass times the acceleration: 0.05 kg * 0.5 m/s² = 2.5 x 10^-2 N.

Question 4

Three blocks (A,B,C), each having mass M, are connected by strings as shown. Block C is pulled to the right by a force  that causes the entire system to accelerate. Neglecting friction, the net force acting on block B is:

Accepted Answer

The answer of Three blocks (A,B,C), each having mass M,...

Question 5

When a 25-kg crate is pushed across a frictionless horizontal floor with a force of 200 N, directed 20  below the horizontal, the magnitude of the normal force of the floor on the crate is:

Accepted Answer

The answer of When a 25-kg crate is pushed across...

Question 6

Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force  as shown. The magnitude of the force of either of these blocks on the other is:

Accepted Answer

The answer of Two blocks with masses m and M...

Question 7

A crane operator lowers a 16,000 N steel ball with a downward acceleration of 3 m/s². The tension in the cable is:

Accepted Answer

The tension in the cable can be found using the equation:

T = m(g + a)

where T is the tension, m is the mass of the steel ball (in kg), g is the acceleration due to gravity (9.8 m/s^2), and a is the downward acceleration of the ball.

First, we need to convert the weight of the ball from N to kg:

m = weight/g = 16000/9.8 = 1632.65 kg

Next, we can plug in the values for m, g, and a:

T = (1632.65 kg)(9.8 m/s^2 + 3 m/s^2)
T = 1632.65 kg * 12.8 m/s^2
T = 20928.72 N

Rounding to the nearest thousand, we get:

Answer: B) 11,000 N

Question 8

A car moves horizontally with a constant acceleration of 3 m/s². A ball is suspended by a string from the ceiling of the car; the ball does not swing, being at rest with respect to the car. What angle does the string make with the vertical?

Accepted Answer

The tension in the string can be resolved into two components: one vertical and one horizontal. The vertical component supports the weight of the ball, while the horizontal component causes the ball to accelerate horizontally with the same acceleration as the car.

Since the ball remains at rest with respect to the car, the vertical component of tension must exactly counteract the weight of the ball. Therefore, the vertical component of tension is equal to mg, where m is the mass of the ball and g is the acceleration due to gravity.

The horizontal component of tension is equal to ma, where a is the horizontal acceleration of the car and the ball.

Since the string must be at an angle to provide both a horizontal and vertical component of tension, we can use trigonometry to find the angle.

tan(theta) = (horizontal component of tension)/(vertical component of tension)
tan(theta) = (ma)/(mg)
tan(theta) = a/g
tan(theta) = 3/9.81

Solving for theta:
theta = tan^-1(3/9.81)
theta ≈ 17°

Therefore, the angle that the string makes with the vertical is approximately 17°.

Question 9

Two blocks weighing 250 N and 350 N respectively, are connected by a string that passes over a massless pulley as shown. The tension in the string is:

Accepted Answer

The answer of Two blocks weighing 250 N and 350...

Question 10

A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by the:

Accepted Answer

The reaction to the force of gravity on the block (the Earth pulling on the block) is the force exerted by the block on the Earth. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Thus, the block exerts a force on the Earth equal in magnitude and opposite in direction to the force that the Earth exerts on it.

Question 11

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The force of book Z on book Y is:

Accepted Answer

The force of book Z on book Y is equal to the weight of book Y, which is 9 N.

Question 12

A 1-N pendulum bob is held at an angle $\theta$from the vertical by a 2-N horizontal force F as shown. The tension in the string supporting the pendulum bob (in newtons) is:

Accepted Answer

Since the force F is horizontal, it does not affect the tension in the string supporting the pendulum bob. The bob is acted upon only by its weight (which is 1 N) and the tension in the string. Resolving forces vertically, we have:
T cos θ = mg
where T is the tension in the string, θ is the angle between the string and the vertical, and m is the mass of the pendulum bob (which is not given but cancels out). Solving for T, we get:
T = mg/cos θ = 1 N/cos (10°) ≈ 11.09 N
Therefore, the correct choice is C.

Question 13

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is:

Accepted Answer

The net force acting on book Y is zero, since the forces acting on it are balanced. Book X is exerting a force of 4 N down and book Z is exerting a force of 4 N up, resulting in a net force of zero.

Question 14

A block slides down a frictionless plane that makes an angle of 30 with the horizontal. The acceleration of the block (in cm/s²) is:

Accepted Answer

The acceleration of the block down the plane can be found using the formula a = g*sin(theta), where g is the acceleration due to gravity (980 cm/s^2) and theta is the angle of the plane. Plugging in the values, we get a = 980*sin(30) = 490 cm/s^2. Therefore, the best choice is E.

Question 15

The "reaction" force does not cancel the "action" force because:

Accepted Answer

The reaction force is exerted on a different body than the action force, and therefore cannot cancel it out.

Question 16

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the rope is:

Accepted Answer

The force of the block on the rope is equal in magnitude, but opposite in direction, to the force of the rope on the block. The force can be found using Newton's second law, F = ma, where F is the force, m is the mass, and a is the acceleration. Thus, F = (5 kg)(2.8 m/s^2) = 14 N, but since the force is in the opposite direction of the acceleration, the answer is 14 N downward, which corresponds to choice D.

Question 17

A 5-kg block is suspended by a rope from the ceiling of an elevator accelerates downward at 3.0 m/s². The tension force of the rope on the block is:

Accepted Answer

The tension force in the rope can be found by analyzing the forces on the block. There are two forces acting on the block: the force due to gravity (weight) of 5g = 5 x 9.81 = 49.05 N, acting downward, and the tension force in the rope, acting upward. 
When the elevator accelerates downward, the tension force decreases, because the net force on the block is in the same direction as the force due to gravity. 
Using Newton's second law, F_net = ma, where F_net is the net force on the block, m is the mass of the block, and a is the acceleration of the block, we can find the tension force: 
F_net = T - mg = ma 
T = ma + mg = m(a + g) 
T = 5(3 + 9.81) = 54.05 N 
Since the acceleration is downward, the tension force is acting downward as well, so the answer is C) 34 N, down.

Question 18

A book rests on a table, exerting a downward force on the table. The reaction to this force is:

Accepted Answer

According to Newton's third law of motion, "for every action, there is an equal and opposite reaction". In this case, the action is the book exerting a downward force on the table, and the reaction is the table exerting an upward force on the book. Therefore, the correct answer is B) the force of the table on the book.

Question 19

A man weighing 700 Nb is in an elevator that is accelerating upward at 4 m/s². The force exerted on him by the elevator floor is:

Accepted Answer

The force exerted on the man by the elevator floor is the normal force, which is equal to the gravitational force plus the force due to the elevator's acceleration. The gravitational force is 700 N (weight), and the additional force due to acceleration is mass times acceleration (m*a). First, convert the weight to mass: 700 N = m * 9.8 m/s², so m = 71.43 kg. The additional force is 71.43 kg * 4 m/s² = 285.72 N. The total force is 700 N + 285.72 N = 985.72 N, which rounds to 990 N.

Question 20

You stand on a spring scaleon the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

Accepted Answer

When the elevator moves upward with increasing speed, your apparent weight increases due to the acceleration of the elevator adding to the force of gravity. This results in the highest scale reading.

Quiz 5: Force and Motion I

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the Earth is:

You stand on a spring scale on the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

A short 10-g string is used to pull a 50-g toy across a frictionless horizontal surface. If a 3.0 * 10^-²-N force is applied horizontally to the free end, the force of the string on the toy, at the other end, is:

Three blocks (A,B,C) , each having mass M, are connected by strings as shown. Block C is pulled to the right by a force that causes the entire system to accelerate. Neglecting friction, the net force acting on block B is:

When a 25-kg crate is pushed across a frictionless horizontal floor with a force of 200 N, directed 20 below the horizontal, the magnitude of the normal force of the floor on the crate is:

Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force as shown. The magnitude of the force of either of these blocks on the other is:

A crane operator lowers a 16,000 N steel ball with a downward acceleration of 3 m/s². The tension in the cable is:

A car moves horizontally with a constant acceleration of 3 m/s². A ball is suspended by a string from the ceiling of the car; the ball does not swing, being at rest with respect to the car. What angle does the string make with the vertical?

Two blocks weighing 250 N and 350 N respectively, are connected by a string that passes over a massless pulley as shown. The tension in the string is:

A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by the:

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The force of book Z on book Y is:

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is:

A block slides down a frictionless plane that makes an angle of 30 with the horizontal. The acceleration of the block (in cm/s²) is:

The "reaction" force does not cancel the "action" force because:

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the rope is:

A 5-kg block is suspended by a rope from the ceiling of an elevator accelerates downward at 3.0 m/s². The tension force of the rope on the block is:

A book rests on a table, exerting a downward force on the table. The reaction to this force is:

A man weighing 700 Nb is in an elevator that is accelerating upward at 4 m/s². The force exerted on him by the elevator floor is:

You stand on a spring scaleon the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

Quiz 5: Force and Motion I

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s2 by means of a rope. The force of the block on the Earth is:

You stand on a spring scale on the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

A short 10-g string is used to pull a 50-g toy across a frictionless horizontal surface. If a 3.0 * 10-2-N force is applied horizontally to the free end, the force of the string on the toy, at the other end, is:

Three blocks (A,B,C) , each having mass M, are connected by strings as shown. Block C is pulled to the right by a force that causes the entire system to accelerate. Neglecting friction, the net force acting on block B is:

When a 25-kg crate is pushed across a frictionless horizontal floor with a force of 200 N, directed 20 below the horizontal, the magnitude of the normal force of the floor on the crate is:

Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force as shown. The magnitude of the force of either of these blocks on the other is:

A crane operator lowers a 16,000 N steel ball with a downward acceleration of 3 m/s2. The tension in the cable is:

A car moves horizontally with a constant acceleration of 3 m/s2. A ball is suspended by a string from the ceiling of the car; the ball does not swing, being at rest with respect to the car. What angle does the string make with the vertical?

Two blocks weighing 250 N and 350 N respectively, are connected by a string that passes over a massless pulley as shown. The tension in the string is:

A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by the:

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The force of book Z on book Y is:

A 1-N pendulum bob is held at an angle θ\thetaθ from the vertical by a 2-N horizontal force F as shown. The tension in the string supporting the pendulum bob (in newtons) is:

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is:

A block slides down a frictionless plane that makes an angle of 30 with the horizontal. The acceleration of the block (in cm/s2) is:

The "reaction" force does not cancel the "action" force because:

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s2 by means of a rope. The force of the block on the rope is:

A 5-kg block is suspended by a rope from the ceiling of an elevator accelerates downward at 3.0 m/s2. The tension force of the rope on the block is:

A book rests on a table, exerting a downward force on the table. The reaction to this force is:

A man weighing 700 Nb is in an elevator that is accelerating upward at 4 m/s2. The force exerted on him by the elevator floor is:

You stand on a spring scaleon the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the Earth is:

A short 10-g string is used to pull a 50-g toy across a frictionless horizontal surface. If a 3.0 * 10^-²-N force is applied horizontally to the free end, the force of the string on the toy, at the other end, is:

A crane operator lowers a 16,000 N steel ball with a downward acceleration of 3 m/s². The tension in the cable is:

A car moves horizontally with a constant acceleration of 3 m/s². A ball is suspended by a string from the ceiling of the car; the ball does not swing, being at rest with respect to the car. What angle does the string make with the vertical?

A block slides down a frictionless plane that makes an angle of 30 with the horizontal. The acceleration of the block (in cm/s²) is:

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the rope is:

A 5-kg block is suspended by a rope from the ceiling of an elevator accelerates downward at 3.0 m/s². The tension force of the rope on the block is:

A man weighing 700 Nb is in an elevator that is accelerating upward at 4 m/s². The force exerted on him by the elevator floor is: