Q: A 6-kg bucket of water is being pulled straight up by a string at a constant speed. What is the tension in the rope?

$$T = 6 \times 9.8 = 58.8\ \mathrm{N}$$

Q: A 3-kg book is raised upward with an acceleration of $$2\ \mathrm{m/s^2$}. $$What is the magnitude of the force your hand exerts on the book?

$$F = 3 \times (9.8 + 2) = 35.4\ \mathrm{N}$$

Question 1

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

Accepted Answer

An object will remain at rest or move with constant velocity unless acted upon by a net external force.

Question 2

A hockey puck slides across a frictionless ice surface at constant velocity. What can you conclude about the net force acting on the puck?

Accepted Answer

The net force acting on the puck is zero.

Question 3

A block of mass $$m is $$pulled up a frictionless incline at angle $$	heta by a $$string connected to a hanging mass $$M. If $$the incline becomes vertical ($$	heta = 90^\circ$$), for what value of $$M$$ will the acceleration of the system be zero?

Accepted Answer

$$M = m$$

Question 4

In the system shown, a block of mass $$m_1$$ hangs vertically and is connected by a massless string over a frictionless pulley to a block of mass $$m_2 on an $$inclined plane. If the tension in the string on both sides of the pulley is $$T$$, what can you conclude?

Accepted Answer

The tension is the same on both sides because the pulley and string are massless and frictionless.

Question 5

A 6-kg bucket of water is being pulled straight up by a string at a constant speed. What is the tension in the rope?

Accepted Answer

$$T = 6 	imes 9.8 = 58.8\ \mathrm{N}$$

Question 6

A 3-kg book is raised upward with an acceleration of $$2\ \mathrm{m/s^2$}. $$What is the magnitude of the force your hand exerts on the book?

Accepted Answer

$$F = 3 	imes (9.8 + 2) = 35.4\ \mathrm{N}$$

Question 7

A rope of length $$L$$ and mass per unit length $$\lambda$$ hangs vertically. What is the tension at a point $$y$$ above the bottom of the rope?

Accepted Answer

$$T(y) = \lambda g (L - y)$$

Question 8

A car is moving to the left with constant velocity. What can you conclude about the net force acting on the car?

Accepted Answer

The net force acting on the car is zero.

Question 9

Two forces, $$F_1 = 10$$\ \mathrm{N}$$ to the right and F_2$ = 4\ \mathrm{N} to $$the left, act on an object. What is the magnitude and direction of the net force?

Accepted Answer

$$6\ \mathrm{N} to $$the right

Question 10

Which of the following is a correct statement of Newton's Third Law?

Accepted Answer

For every action, there is an equal and opposite reaction.

Question 11

A block is pulled along a frictionless surface by a constant horizontal force. What is true about its motion?

Accepted Answer

It moves with a constant nonzero acceleration.

Question 12

A 20-kg shopping cart is pushed with a force of $$86\ \mathrm{N} at$$ $$30^\circ$$ above the horizontal. What is the horizontal acceleration of the cart? (Assume no friction.)

Accepted Answer

$$a = \frac{86 \cos 30^\circ}{20} = 3.7\ \mathrm{m/s^2$}$$

Question 13

Three blocks (A: $$1.50\ \mathrm{kg}$$, B: $$2.50\ \mathrm{kg}$$, C: $$1.20\ \mathrm{kg}) $$are pushed to the right with an acceleration of $$1.12\ \mathrm{m/s^2$}. $$What is the force that block B exerts on block C?

Accepted Answer

$$F = 1.34\ \mathrm{N}$$

Question 14

Which of the following is NOT a correct application of Newton's Third Law?

Accepted Answer

The force of a car engine on the road and the force of the road on the car are equal in magnitude and opposite in direction.

Question 15

A block of mass $$m is $$acted upon by two forces: $$F_1 ($$left) and $$F_2 ($$right). If $$F_1$$ = $$F_2$$, what can you say about the block's motion?

Accepted Answer

The net force is zero, so the block moves with constant velocity (which may be zero).

Question 16

A 1000-N elevator is suspended by a cable and is moving downward, slowing at $$3\ \mathrm{m/s^2$}. $$What is the tension in the cable?

Accepted Answer

$$T = 1300\ \mathrm{N}$$

Question 17

Which of the following force diagrams (from the set labeled 1-6) could represent a situation where the net force is zero?

Accepted Answer

Diagram 5

Question 18

A person on a swing is at rest at an angle of $$25^\circ$$ from the vertical. Which forces act on the person?

Accepted Answer

Gravity downward and tension along the rope

Step-by-Step Guidance for Newton's Laws and Force Diagrams

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