Question 1

A 10 kg block is pulled to the right by a force of 70 N and to the left by a force of 20 N. What is the acceleration of the block? (Assume right is positive.)

Accepted Answer

$$a = 5\ \mathrm{m/s^2$}$$

Question 2

A 5 kg box is pushed to the right with a force of 20 N across a flat table. The force of kinetic friction is 8 N. What is the acceleration of the box?

Accepted Answer

$$a = 2.4\ \mathrm{m/s^2$}$$

Question 3

A 1000-kg rocket is accelerating vertically upward. The engines provide 25,000 N of thrust, gravity exerts 10,000 N downward, and air resistance is 5,000 N downward. What is the rocket’s acceleration?

Accepted Answer

$$a = 10\ \mathrm{m/s^2$}$$

Question 4

Which of the following is NOT an action-reaction pair according to Newton’s Third Law?

Accepted Answer

Weight of the book & normal force on the book

Question 5

A 3-kg bucket is being pulled upwards by a cord with a tension of 35 N. What is the acceleration of the bucket? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = 1.9\ \mathrm{m/s^2$}$$

Question 6

A 20 kg block on a frictionless surface is pushed from rest to 30 m/s in 6 s. What is the magnitude of the applied force?

Accepted Answer

$$F = 100\ \mathrm{N}$$

Question 7

A 3-kg box is lowered on a string at a constant speed. What is the tension in the string? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$T = 29.4\ \mathrm{N}$$

Question 8

A 5.1 kg block is pulled by a 10 N force at 37° above the horizontal. Assuming no friction, what is the normal force on the block? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$N = 44.2\ \mathrm{N}$$

Question 9

A 2-kg box is dropped straight down from a building. A steady horizontal wind exerts a constant force of 3 N on the box as it falls. What is the direction of the box’s acceleration?

Accepted Answer

$$81^\circ$$ below horizontal

Question 10

A 4 kg block on a frictionless table is connected to a 2 kg block hanging off the table by a cable and massless pulley. What is the acceleration of the system? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = 3.27\ \mathrm{m/s^2$}$$

Question 11

A 10,000 N Mars Rover weighs 3,790 N on Mars. What is the gravitational acceleration on Mars?

Accepted Answer

$$g_{Mars} = 3.79\ \mathrm{m/s^2$}$$

Question 12

A chandelier is supported from the ceiling by 2 chains, each making a 30° angle with the vertical. The tension in each chain is 50 N. What is the mass of the chandelier? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$m = 8.8\ \mathrm{kg}$$

Question 13

Which of the following statements about the normal force is correct?

Accepted Answer

The normal force is always perpendicular to the surface.

Question 14

Two blocks of mass 3 kg and 5 kg are connected by a string and pulled horizontally with a force of 30 N. What is the acceleration of the system?

Accepted Answer

$$a = 3.75\ \mathrm{m/s^2$}$$

Question 15

A loudspeaker is held in place by four vertical cables. The tension in each cable is 30 N. What is the mass of the loudspeaker? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$m = 12.2\ \mathrm{kg}$$

Intro to Forces (Dynamics): Newton’s Laws and Force Analysis

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