Force and Motion Review

Why does an object in motion stay in motion unless acted on by an unbalanced force?

• because forces are what stop and start motion

• because balanced forces can not exist in nature

• because motion is the inherent state of all matter

• because motion, once begun, continues to accelerate

A train rolls to a stop along a horizontal track without the conductor applying the brakes. What answer choice BEST explains why this occurred?

• The train ran out of momentum.

• The opposing force of friction stopped the train.

• The natural state of the train is not to be in motion.

• The force of gravity slowed the train until it stopped.

This graph represents the motion of a car while driving over a short distance. Which statement accurately describes the motion of the car in this graph?

• It is going forwards slow, then it is going forwards fast.

• It is going forwards fast, then it is going forwards slowly.

• It is going backwards slow, then it is going backwards fast.

• It is going backwards fast, then it is going backwards slowly.

John and Caroline go out for a walk one day. This graph represents the distance they traveled over time.

During what part of their walk are they not moving?

• From 0 to 0.75 hours

• From 1.25 to 2.0 hours

• From 0.75 to 1.25 hours

• They are moving the entire time.

A train engineer started the train from a standstill and sped up to 5 meters per second, she then rounded a corner at a constant speed. She then sped the train up to 10 meters per second on the next straightaway. Next, the train chugged around another bend at 10 m/sec, and then its speed slowed to 5 meters per second after coming out of the bend. Finally, the train reached the station, and the engineer applied the brakes and brought the engine to a stop. How many times did the train accelerate?

• 2

• 4

• 5

• 6

Imagine you are on the top of a mountain with four basketballs. The mass of the four basketballs are 100 kilograms, 200 kilograms, 300 kilograms, and 400 kilograms. If the basketballs rolled down the hill, which one would supply the greatest force at the bottom of the mountain (assume that their velocities were equal at the bottom of the mountain)?

• 100 kilogram basketball

• 200 kilogram basketball

• 300 kilogram basketball

• 400 kilogram basketball

At the county fair, Carrie and Sam climbed up on the carousel horses. Around and around they went; the horses also bobbed up and down. When they got off of the carousel, Carrie told Sam they had been accelerating during their ride. Sam disagreed; they had been moving at a constant speed. Whose response is fully correct, and why?

• Carrie is, because the carousel changed speed when it started and stopped.

• Sam is, because the horses never moved from their position on the carousel.

• Carrie is, because velocity includes speed plus direction, and both changed.

• Sam is, they did not accelerate since their speed remained constant for the ride.

The Smith family is traveling in their car at 50 km/h due east. Mr. Smith is using cruise control to maintain a constant speed. Describe the net force acting on the Smith car.

• Net force equals zero.

• Net forces are unbalanced.

• Net force is positive and to the east.

• There is no way to determine net force.

Consider the free body diagram. If the sum of the tension forces is equal to the force of gravity, which description BEST applies?

• A book is at rest on a tabletop.

• A physics student rests a backpack upon one shoulder.

• A girl hangs by both hands, motionless, from a pull up bar.

• A girl falls slowly to Earth while strapped to a parachute.

Consider this line graph that represents speed in meters/second. The X-axis is labelled in seconds; the Y-axis is labelled in meters. Imagine that the moving object stops after 2.5 seconds and stays stopped for 0.5 seconds. What would the line for that time interval look like on this graph?

• curve downward to Y equals 3

• straight, diagonal, negative slope to {14, 3}

• straight, diagonal, positive slope to {3, 15}

• straight and horizontal at Y equals 14, to {3, 14}