Q: A jet with mass $$m = 51,000\ \mathrm{kg}$$ accelerates down a runway of length $$d = 940\ \mathrm{m} to $$reach a takeoff speed of $$v = 70\ \mathrm{m/s}. $$Assuming constant acceleration, what is the acceleration $$a of $$the jet?

$$a = \frac{v^2$}{2d} = \frac{(70)^2$}{2 \times 940} \approx 2.61\ \mathrm{m/s^2$}$$

Question 1

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

Accepted Answer

An object at rest will remain at rest, and an object in motion will continue moving in a straight line at constant speed unless acted upon by a net force.

Question 2

A hockey puck slides across a frictionless ice surface. Which statement is true about its motion?

Accepted Answer

It will continue moving at constant velocity unless a force acts on it.

Question 3

Which of the following is an example of a long-range force?

Accepted Answer

Gravitational force between the Earth and an apple

Question 4

A 2 kg block is pulled by a constant force of 10 N on a frictionless surface. What is its acceleration?

Accepted Answer

$$a = \frac{10}{2} = 5\ \mathrm{m/s^2$}$$

Question 5

Which force is responsible for keeping a person from slipping while walking?

Accepted Answer

Static friction

Question 6

A jet with mass $$m = 51,000\ \mathrm{kg}$$ accelerates down a runway of length $$d = 940\ \mathrm{m} to $$reach a takeoff speed of $$v = 70\ \mathrm{m/s}. $$Assuming constant acceleration, what is the acceleration $$a of $$the jet?

Accepted Answer

$$a = \frac{v^2$}{2d} = \frac{(70)^2$}{2 	imes 940} \approx 2.61\ \mathrm{m/s^2$}$$

Question 7

If the net force on an object is zero, which of the following must be true?

Accepted Answer

The object will move at constant velocity or remain at rest.

Question 8

Which of the following best describes Newton's Third Law?

Accepted Answer

For every force, there is an equal and opposite force acting on a different object.

Question 9

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

Accepted Answer

The applied force is equal to the friction force.

Question 10

A car crashes into a wall and comes to a sudden stop. The dummy inside continues moving forward until it hits the dashboard. Which law explains the dummy's motion?

Accepted Answer

Newton's First Law

Question 11

Which of the following is the correct vector equation for the net force acting on an object?

Accepted Answer

$$\vec{F}_{\mathrm{net}} = \vec{F}_1 + \vec{F}_2 + \vec{F}_3 + \ldots$$

Question 12

A compressed spring exerts a force on a block. What type of force is this?

Accepted Answer

Spring force

Question 13

Which of the following is true about the direction of the weight vector for an object near Earth's surface?

Accepted Answer

It always points vertically downward.

Question 14

A block of mass $$m is $$acted upon by a net force $$F. $$According to Newton's Second Law, what is the acceleration $$a$$?

Accepted Answer

$$a = \frac{F}{m}$$

Question 15

A rocket launches by expelling hot gases downward. What is the reaction force according to Newton's Third Law?

Accepted Answer

The rocket pushes the gases downward, and the gases push the rocket upward.

Question 16

A box is at rest on a table. Which force balances the weight of the box?

Accepted Answer

Normal force

Question 17

A car of mass $$m$$ accelerates at $$a$$ due to a net force $$F. If $$the mass is doubled and the same force is applied, what happens to the acceleration?

Accepted Answer

It halves.

Question 18

Which of the following is true about action/reaction pairs?

Accepted Answer

They act on different objects and are equal in magnitude and opposite in direction.

Question 19

A block slides across a rough surface and slows down. Which force is responsible for this?

Accepted Answer

Kinetic friction

Question 20

A jet engine produces a thrust of $$67,000\ \mathrm{N}. If $$the plane has two engines, what is the total thrust?

Accepted Answer

$$134,000\ \mathrm{N}$$

Forces and Newton’s Laws of Motion – Study Notes

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