Q: A 10 kg object is initially at rest and is pushed with a constant force so that it reaches a velocity of 50 m/s in 10 seconds. What is the magnitude of the net force applied to the object?

$$F = 50\ \mathrm{kg} \times 5\ \mathrm{m/s^2$} = 50\ \mathrm{N}$$

Q: A 5 kg block is pulled across a horizontal surface with a force of 30 N. The coefficient of kinetic friction between the block and the surface is 0.2. What is the acceleration of the block?

$$a = \frac{30 - (0.2 \times 5 \times 9.8)}{5} = 4.08\ \mathrm{m/s^2$}$$

Q: A car of mass 1000 kg rounds a curve of radius 50 m at a speed of 20 m/s. What is the magnitude of the centripetal force acting on the car?

$$F_c = \frac{1000 \times 20^2$}{50} = 8000\ \mathrm{N}$$

Q: A 2 kg object is suspended from a rope. What is the tension in the rope if the object is at rest?

$$T = 2 \times 9.8 = 19.6\ \mathrm{N}$$

Q: A 4 kg block is at rest on a horizontal surface. The coefficient of static friction is 0.5. What is the maximum force that can be applied horizontally before the block starts to move?

$$F_{max} = 0.5 \times 4 \times 9.8 = 19.6\ \mathrm{N}$$

Question 1

A 10 kg object is initially at rest and is pushed with a constant force so that it reaches a velocity of 50 m/s in 10 seconds. What is the magnitude of the net force applied to the object?

Accepted Answer

$$F = 50\ \mathrm{kg} 	imes 5\ \mathrm{m/s^2$} = 50\ \mathrm{N}$$

Question 2

Which of the following best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or in uniform motion unless acted upon by a net external force.

Question 3

A 5 kg block is pulled across a horizontal surface with a force of 30 N. The coefficient of kinetic friction between the block and the surface is 0.2. What is the acceleration of the block?

Accepted Answer

$$a = \frac{30 - (0.2 	imes 5 	imes 9.8)}{5} = 4.08\ \mathrm{m/s^2$}$$

Question 4

Which of the following is NOT a characteristic of an inertial reference frame?

Accepted Answer

It is accelerating relative to the stars.

Question 5

A car of mass 1000 kg rounds a curve of radius 50 m at a speed of 20 m/s. What is the magnitude of the centripetal force acting on the car?

Accepted Answer

$$F_c = \frac{1000 	imes 20^2$}{50} = 8000\ \mathrm{N}$$

Question 6

Two blocks, one of mass 3 kg and the other of mass 5 kg, are connected by a light rope and pulled horizontally with a force of 40 N. If the surface is frictionless, what is the acceleration of the system?

Accepted Answer

$$a = \frac{40}{8} = 5\ \mathrm{m/s^2$}$$

Question 7

A 2 kg object is suspended from a rope. What is the tension in the rope if the object is at rest?

Accepted Answer

$$T = 2 	imes 9.8 = 19.6\ \mathrm{N}$$

Question 8

Which of the following is an example of Newton's Third Law?

Accepted Answer

A swimmer pushes water backward, and the water pushes the swimmer forward.

Question 9

A 4 kg block is at rest on a horizontal surface. The coefficient of static friction is 0.5. What is the maximum force that can be applied horizontally before the block starts to move?

Accepted Answer

$$F_{max} = 0.5 	imes 4 	imes 9.8 = 19.6\ \mathrm{N}$$

Question 10

A 1 kg puck moves in a circle of radius 2 m at a constant speed of 3 m/s on a frictionless surface. What is the magnitude of the centripetal acceleration?

Accepted Answer

$$a_c = \frac{3^2$}{2} = 4.5\ \mathrm{m/s^2$}$$

Question 11

A 10 kg box is pushed across a rough floor with a force of 60 N. The coefficient of kinetic friction is 0.3. What is the net force on the box?

Accepted Answer

$$F_{net} = 60 - (0.3 	imes 10 	imes 9.8) = 30.6\ \mathrm{N}$$

Question 12

Which of the following statements about friction is correct?

Accepted Answer

Kinetic friction acts when an object is moving, and its magnitude is $$f_k = \mu_k N.$$

Question 13

A 2 kg block is attached to a 3 kg block by a rope and pulled with a force of 25 N. If the coefficient of kinetic friction is 0.1 for both blocks, what is the acceleration of the system?

Accepted Answer

$$a = \frac{25 - 0.1 	imes (2+3) 	imes 9.8}{2+3} = 4.04\ \mathrm{m/s^2$}$$

Question 14

Which of the following is NOT a third law force pair?

Accepted Answer

The gravitational force Earth exerts on a falling apple and the normal force the ground exerts on the apple.

Question 15

A 6 kg block is on a frictionless table and is connected by a string to a 4 kg block hanging off the edge. What is the acceleration of the system? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = \frac{4 	imes 9.8}{6+4} = 3.92\ \mathrm{m/s^2$}$$

Question 16

A 70 kg astronaut in space pushes against a 140 kg satellite. If the astronaut moves away at 2 m/s, what is the velocity of the satellite?

Accepted Answer

$$v = -1\ \mathrm{m/s}$$

Question 17

A 5 kg block is at rest on a table. What is the normal force acting on the block?

Accepted Answer

$$N = 5 	imes 9.8 = 49\ \mathrm{N}$$

Question 18

A 2 kg object is moving in a circle of radius 0.5 m at a speed of 4 m/s. What is the magnitude of the centripetal force?

Accepted Answer

$$F_c = \frac{2 	imes 4^2$}{0.5} = 64\ \mathrm{N}$$

Question 19

A 3 kg block is pulled by a rope at an angle of 30° above the horizontal with a force of 20 N. What is the horizontal component of the force?

Accepted Answer

$$F_x = 20 \cos 30^\circ = 17.32\ \mathrm{N}$$

Newton's Laws of Motion and Circular Motion: Structured Study Notes

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