Q: A woman stands on a scale in an elevator that is accelerating downward at $$5.00\ \text{m/s}^2. $$Her mass is $$60.0\ \text{kg}. $$What is her apparent weight?

$$N = m(g - a) = 60.0 \times (9.8 - 5.0) = 288\ \text{N}$$

Question 1

A block of mass $$m is $$pulled to the right on a frictionless surface with a constant force $$\sum \vec{F}. $$What is the acceleration $$\vec{a} of $$the block?

Accepted Answer

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

Question 2

A motorcycle with a powerful engine (large $$F) $$and lightweight frame (small $$m) $$accelerates quickly. Which law best explains this observation?

Accepted Answer

Newton's Second Law: $$\sum \vec{F} = m \vec{a}$$

Question 3

A car is moving at constant velocity toward a wall. According to Newton's First Law, what will happen if no net force acts on the car?

Accepted Answer

The car will continue moving at constant velocity.

Question 4

A woman stands on a scale in an elevator that is accelerating downward at $$5.00\ 	ext{m/s}^2. $$Her mass is $$60.0\ 	ext{kg}. $$What is her apparent weight?

Accepted Answer

$$N = m(g - a) = 60.0 	imes (9.8 - 5.0) = 288\ 	ext{N}$$

Question 5

Which of the following is the correct action-reaction force pair when a soccer ball is kicked?

Accepted Answer

Force of foot on ball and force of ball on foot

Question 6

An apple rests on a table. Which two forces act on the apple?

Accepted Answer

The normal force from the table and the gravitational force from the Earth

Question 7

A person pulls on a rope attached to two crates (each $$100\ 	ext{kg}) in a $$line. Which rope is most likely to break first if the person pulls very hard?

Accepted Answer

Rope 1 (between person and first crate)

Question 8

A woman in an elevator sees her weight decrease suddenly on the scale. What does this indicate?

Accepted Answer

The elevator has started accelerating downward.

Question 9

Which of the following is NOT an inertial reference frame?

Accepted Answer

A bus that is accelerating on a straight road

Question 10

A block is pulled by a string on a frictionless surface. The string is cut. What happens to the block's motion after the cut?

Accepted Answer

It moves at a constant speed.

Question 11

A woman stands on a scale in an elevator moving downward with decreasing speed. What is true about the normal force $$N$$ acting on her?

Accepted Answer

$$N \u003e mg$$

Question 12

The force of gravity acting on you by the Earth is $$\vec{F}_{	ext{Earth on you}}. $$What is the reaction force according to Newton's Third Law?

Accepted Answer

The force of gravity acting on the Earth by you ($$\vec{F}_{	ext{you on Earth}})$$

Question 13

A stalled car is being pushed up a hill at constant velocity by three people. What is the net force on the car?

Accepted Answer

Zero

Question 14

A constant net force acts on an object in the positive x-direction. Which statement is true?

Accepted Answer

The object has a constant acceleration in the +x-direction.

Question 15

Which of the following is a vector quantity?

Accepted Answer

Velocity

Question 16

The sun and Jupiter orbit a common point called the barycenter. Where is the barycenter of the Earth-Sun system located?

Accepted Answer

Inside the Sun

Question 17

A block of mass $$m is $$acted on by two forces: $$\vec{F}_1 to $$the right and $$\vec{F}_2 to $$the left. If $$\vec{F}_1 \u003e \vec{F}_2$$, what is the direction of acceleration?

Accepted Answer

To the right

Question 18

Which equation gives the magnitude of the centripetal acceleration for an object moving in a circle of radius $$r at $$speed $$v$$?

Accepted Answer

$$a_r = \frac{v^2$}{r}$$

Question 19

A person stands on roller skates in a bus that suddenly accelerates forward. What happens to the person in the frame of the bus?

Accepted Answer

The person appears to move backward.

Newton’s Laws of Motion and Applications: Study Notes for University Physics I

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