Physics Motion Quiz 10

Suppose you are in a car that is going around a curve. The speedometer reads a constant 30 mph. Which of the following is NOT true?

• You and the car are accelerating.

• Your acceleration is constantly changing.

• Your velocity is constant.

• Your direction is constantly changing.

• Your speed is constant.

Answer explanation

Your velocity is not constant because, although your speed is constant at 30 mph, you are changing direction while going around the curve. Acceleration occurs due to this change in direction, making your velocity variable.

A soccer ball rolls up a hill, reaches its highest point, then turns around and rolls back to its starting point. During this time the acceleration of the ball:

• is always in the opposite direction of the motion.

• is always in the same direction as the motion.

• changes with the direction of the motion.

• is always directed uphill.

• is always directed downhill.

Answer explanation

The soccer ball's acceleration is always directed downhill due to gravity. As it rolls up, it decelerates, and as it rolls back down, it accelerates, but the acceleration remains directed downhill throughout the motion.

Tags

NGSS.MS-PS2-2

Ed rides his mountain bike down a hillside as follows: During the first 3 seconds, his speed goes from 0 m/sec to 4 m/sec. After 3 seconds, Ed travels at 4 m/sec for the rest of his trip down the hill. When was Ed accelerating?

• During the first 3 seconds.

• During the entire trip.

• During the entire trip except at t = 0 sec.

• At t = 3 seconds.

• After t = 3 seconds.

Answer explanation

Ed was accelerating during the first 3 seconds as his speed increased from 0 m/sec to 4 m/sec. After that, he maintained a constant speed of 4 m/sec, indicating no further acceleration.

A ball rolls toward a wall at constant speed, hits the wall, then rolls back at constant speed. When, if ever, is the object accelerating?

• The object accelerates when it changes direction.

• The object never accelerates because it is always traveling with constant speed.

• If the speed doesn't change when the object hits the wall, then there is no acceleration.

• Can't tell, because we need to know the actual speed of the ball.

Answer explanation

The object accelerates when it changes direction. Acceleration occurs not only when speed changes but also when the direction of motion changes, such as when the ball hits the wall and rolls back.

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-1

If an automobile’s velocity changes from 25 m/s to 15 m/s in 2 s, what is its acceleration?

• 5 m/s/s

• -5 m/s/s

• 10 m/s/s

• -10 m/s/s

Answer explanation

Acceleration is calculated as the change in velocity divided by the time taken. Here, the change is (15 m/s - 25 m/s) = -10 m/s over 2 s, giving an acceleration of -10 m/s / 2 s = -5 m/s², which is the correct answer.

An automobile accelerates at 5 m/s/s. How much time is required for the automobile to reach a speed of 30 m/s if it starts from rest?

• 0.17 s

• 5 s

• 6 s

• 150 s

Answer explanation

To find the time, use the formula: time = (final speed - initial speed) / acceleration. Here, time = (30 m/s - 0 m/s) / 5 m/s² = 6 s. Thus, the correct answer is 6 s.

Some motion data for a snail is shown in the table. What is the snail’s acceleration? Record the number without units.

Answer explanation

The snail's acceleration is calculated as the change in velocity over time. If the motion data shows constant speed, the change in velocity is zero, resulting in an acceleration of 0. Thus, the correct answer is 0.

Some motion data for a Honda Accord is shown in the table. What is the car’s acceleration? Record the number first with direction (no space and no comma).

Answer explanation

The acceleration of the Honda Accord is calculated as the change in velocity over time. If the motion data indicates no change in speed, the acceleration is 0. Therefore, the correct answer is 0.

A speed vs. time graph of a bicycle's motion is shown. Which statement best describes the motion of the bike?

• The bike starts from rest, then moves with a constant speed, then slows to a stop.

• The bike starts from rest because the slope is zero, then speeds up toward the origin.

• The bike is first traveling with a high constant speed, then it slows down to a stop.

• The bike is slowing down for the entire trip.

• The bike is first traveling along a flat road, then it begins to go down a hill.

Answer explanation

The correct choice states that the bike is first traveling with a high constant speed, then slows down to a stop. This indicates a decrease in speed over time, which aligns with the graph's representation of motion.

Tags

NGSS.MS-PS3-1

The speed versus time data for a racing turtle is shown in the graph. What is the speed of the turtle at t = 2 minutes?

• 0.5 meter/minute

• 1.0 meter/minute

• 1.5 meters/minute

• 2.5 meters/minute

• 3.0 meters/minute

Answer explanation

At t = 2 minutes, the graph indicates the speed of the turtle is 3.0 meters/minute, which is the highest value shown at that time. Therefore, the correct answer is 3.0 meters/minute.

Tags

NGSS.MS-PS3-1