Question 1

A 1500 kg car is being towed at a constant speed by a rope that makes a 20° angle with the horizontal. If the friction force opposing the car's motion is 320 N, what is the tension in the rope? (Assume equilibrium.)

Accepted Answer

$$T = \frac{320}{\cos 20^\circ}$$

Question 2

Which of the following statements about Newton’s Third Law is correct?

Accepted Answer

Action and reaction forces are always equal in magnitude and opposite in direction.

Question 3

A 46 g golf ball is putted with a speed of 3.0 m/s. If friction exerts a retarding force of 0.10 N, what is the acceleration of the ball?

Accepted Answer

$$a = \frac{0.10}{0.046}$$

Question 4

A person with mass 70 kg stands on a scale in an elevator. The scale reads 750 N as the elevator slows to a stop. What was the direction of the elevator’s motion before stopping?

Accepted Answer

Downward

Question 5

Which equation correctly relates apparent weight $$w_{app} to $$true weight $$w$$ and acceleration $$a in an $$elevator?

Accepted Answer

$$w_{app} = w + ma$$

Question 6

A 1.2 kg book is pressed down on a table with an additional force of 15 N. What is the normal force exerted by the table?

Accepted Answer

$$n = 15 + (1.2 	imes 9.8)$$

Question 7

A skier slides down a frictionless 27° slope. What is the skier’s acceleration?

Accepted Answer

$$a = g \sin 27^\circ$$

Question 8

Which of the following best describes the normal force on an object at rest on a horizontal table?

Accepted Answer

It is always perpendicular to the surface of contact.

Question 9

A 1000 kg elevator accelerates upward with a student of mass 50 kg inside. If the scale reads 549 N, what is the acceleration of the elevator?

Accepted Answer

$$a = \frac{549 - 490}{50}$$

Question 10

Which of the following is true about an object in dynamic equilibrium?

Accepted Answer

It is moving at constant speed in a straight line.

Question 11

A car of mass 1500 kg is towed by a rope at a 20° angle and accelerates from rest to 12 m/s in 10 s. The friction force is 320 N. What is the tension in the rope?

Accepted Answer

$$T = \frac{ma + f}{\cos 20^\circ}$$

Question 12

Which of the following is NOT a correct step in solving a dynamics problem using Newton’s laws?

Accepted Answer

Assume acceleration is always zero.

Question 13

A person in free fall experiences which of the following?

Accepted Answer

Zero apparent weight.

Question 14

On an inclined plane, which component of the gravitational force causes an object to slide down?

Accepted Answer

$$mg \sin 	heta$$

Question 15

A box is pulled to the right at steady speed by a rope that angles upward. What can be said about the normal force compared to the box’s weight?

Accepted Answer

The normal force is less than the box’s weight.

Question 16

Which of the following is a correct statement about mass and weight?

Accepted Answer

Mass is a measure of inertia, while weight is the gravitational force acting on an object.

Question 17

A student pushes down on a book lying on a table. The normal force from the table is:

Accepted Answer

Greater than the book’s weight.

Question 18

Which of the following is the correct vector form of Newton’s Second Law?

Accepted Answer

$$\vec{F}_{net} = m \vec{a}$$

Question 19

A ball is rolling on a horizontal surface and slows down due to friction. Which kinematic equation would you use to find the distance it travels before stopping?

Accepted Answer

$$v_f^2$ = v_0$^2 + 2a(x - x_0$)$$

Lecture 8 Newton's Laws and Applications: Equilibrium, Dynamics, Mass, Weight, and Normal Forces

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