Q: A car of mass $1000 \\ \mathrm{kg}$ is brought to rest from $v = 27.8 \\ \mathrm{m/s}$ (100 km/h) in a distance of $55 \\ \mathrm{m}$. What is the magnitude of the average net force required to stop the car?

$F = 7.0 \\ \times 10^3 \\ \mathrm{N}$

Question 1

A 10 kg box rests on a frictionless horizontal table. If a horizontal force of 30 N is applied to the box, what is the acceleration of the box?

Accepted Answer

$a = 3.0 \ \mathrm{m/s^2}$

Question 2

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

Accepted Answer

An object will remain at rest or move in a straight line at constant speed unless acted upon by a net external force.

Question 3

A 60 kg astronaut weighs less on the Moon than on Earth. Which of the following is true?

Accepted Answer

The astronaut's mass is the same on the Moon and on Earth.

Question 4

A 5 kg object is suspended from a rope. What is the tension in the rope if the object is at rest?

Accepted Answer

$T = 49 \ \mathrm{N}$

Question 5

A person stands on a scale in an elevator accelerating upward at $2.0 \ \mathrm{m/s^2}$. If the person's mass is $70 \ \mathrm{kg}$, what does the scale read?

Accepted Answer

$840 \ \mathrm{N}$

Question 6

A hockey puck slides at constant velocity across a frictionless ice surface. Which of the following is true about the net force acting on the puck?

Accepted Answer

The net force on the puck is zero.

Question 7

A 12 kg box and a 10 kg box are connected by a light cord and rest on a frictionless table. A horizontal force of 44 N is applied to the 10 kg box. What is the acceleration of the system?

Accepted Answer

$a = 2.0 \ \mathrm{m/s^2}$

Question 8

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

Accepted Answer

A rocket is propelled upward by the downward expulsion of hot gases.

Question 9

A spring exerts a force according to Hooke's Law. If a spring with $k = 200 \ \mathrm{N/m}$ is compressed by $0.10 \ \mathrm{m}$, what is the force exerted by the spring?

Accepted Answer

$F = -20 \ \mathrm{N}$

Question 10

A 70 kg woman descends in an elevator that accelerates downward at $0.20g$. What is her apparent weight during this acceleration?

Accepted Answer

$550 \ \mathrm{N}$

Question 11

Which of the following is NOT a contact force?

Accepted Answer

Gravitational force

Question 12

A 10 kg box is at rest on a horizontal frictionless table. What is the normal force exerted by the table on the box?

Accepted Answer

$N = 98 \ \mathrm{N}$

Question 13

A car of mass $1000 \ \mathrm{kg}$ is brought to rest from $v = 27.8 \ \mathrm{m/s}$ (100 km/h) in a distance of $55 \ \mathrm{m}$. What is the magnitude of the average net force required to stop the car?

Accepted Answer

$F = 7.0 \ 	imes 10^3 \ \mathrm{N}$

Question 14

A block is pressed against a wall and remains at rest. Which force balances the block's weight?

Accepted Answer

The friction force from the wall

Question 15

A mass $m$ is hanging from a string in a car that accelerates to the right with acceleration $a$. What is the angle $	heta$ the string makes with the vertical?

Accepted Answer

$	an 	heta = \dfrac{a}{g}$

Question 16

A 15 kg box is at rest on a horizontal surface. A person pushes down on the box with a force of 20 N. What is the normal force exerted by the surface?

Accepted Answer

$N = 167 \ \mathrm{N}$

Question 17

Which of the following best describes the net force acting on an object moving at constant velocity in a straight line?

Accepted Answer

The net force is zero.

Question 18

A man pushes a box across a rough floor at constant speed. Which statement is true about the forces acting on the box?

Accepted Answer

The net force on the box is zero.

Dynamics: Newton’s Laws of Motion – Forces and Applications

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