Question 1

A 6-kg bucket is being pulled straight up by a string at a constant speed. What is the tension in the rope? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$T = 58.8\ \mathrm{N}$$

Question 2

A 10-kg box is at rest on a horizontal frictionless surface. A horizontal force of 20 N is applied to the box. What is the acceleration of the box?

Accepted Answer

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

Question 3

A 4-kg block and a 6-kg block are connected by a light string and pulled with a force $$F on a $$frictionless surface as shown. What is the tension $$T in $$the string between the blocks if $$F = 50\ \mathrm{N}$$?

Accepted Answer

$$T = 30\ \mathrm{N}$$

Question 4

A 15-kg box (A) is in contact with a 5-kg box (B) on a horizontal frictionless surface. A horizontal force of 100 N is applied to box A. What is the force exerted by box A on box B?

Accepted Answer

$$75\ \mathrm{N}$$

Question 5

A toboggan slides down a frictionless hill inclined at angle $$\alpha. $$What is the acceleration of the toboggan?

Accepted Answer

$$a = g\sin\alpha$$

Question 6

A block of mass $$m is $$hanging at rest from a rope. Which of the following is true about the forces acting on the block?

Accepted Answer

The tension in the rope is equal to the weight of the block.

Question 7

A car rounds a flat curve of radius $$R. If $$the coefficient of static friction between the tires and the road is $$\mu_s$$, what is the maximum speed $$v_{max} at $$which the car can take the curve without sliding?

Accepted Answer

$$v_{max} = \sqrt{\mu_s g R}$$

Question 8

A 50-kg skydiver reaches terminal speed while falling through air. If the drag coefficient $$D = 0.25\ \mathrm{kg/m}$$, what is the terminal speed $$v_t$$? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v_t = 44\ \mathrm{m/s}$$

Question 9

Two blocks are connected by a string over an ideal pulley. Block A (on a frictionless $$30^\circ$$ incline) has mass $$m_A$$, and block B (hanging) has mass $$m_B. $$What is the acceleration of the system?

Accepted Answer

$$a = g\frac{m_B - m_A \sin 30^\circ}{m_A + m_B}$$

Question 10

A block of mass $$m$$ slides on a horizontal surface with kinetic friction coefficient $$\mu_k. $$What is the frictional force acting on the block?

Accepted Answer

$$f_k = \mu_k m g$$

Question 11

A monkey and a bunch of bananas, each of mass $$m$$, hang on opposite sides of a frictionless pulley. If the monkey climbs up the rope, what happens to the bananas?

Accepted Answer

The bananas move up with the same acceleration as the monkey.

Question 12

A satellite orbits Earth in a circular orbit of radius $$r. $$What provides the centripetal force required for its motion?

Accepted Answer

The gravitational force between the satellite and Earth.

Question 13

According to Newton’s third law, when you push backward on the ground with your foot while walking, what force propels you forward?

Accepted Answer

The ground pushes forward on your foot with an equal and opposite force.

Question 14

A block of mass $$m is $$falling freely under gravity. What is the net force acting on the block?

Accepted Answer

$$F_{net} = m g$$

Question 15

A 500-N crate is pulled with a 230-N horizontal force to start moving, and then with 200-N to keep it moving at constant velocity. What is the coefficient of kinetic friction?

Accepted Answer

$$\mu_k = 0.40$$

Question 16

Which of the following statements about action-reaction pairs is correct?

Accepted Answer

They always act on two different objects.

Question 17

A block slides down a frictionless incline at angle $$\alpha. $$What is the normal force exerted by the incline on the block?

Accepted Answer

$$n = m g \cos \alpha$$

Question 18

A 0.6-kg mass and a 0.4-kg mass are connected by a string over a frictionless pulley (Atwood machine). What is the acceleration of the system? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = 1.96\ \mathrm{m/s^2$}$$

Newton’s Laws of Motion and Applications: Forces, Friction, and Circular Motion

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