Unit 1: Kinematics Test Review

Consider a deer that runs from point A to point B. The distance the deer runs can be greater than the magnitude of its displacement, but the magnitude of the displacement can never be greater than the distance it runs.

• True

• False

Answer explanation

The statement is true because the distance a deer runs (the total path taken) can exceed the straight-line distance from A to B (displacement), but displacement cannot be greater than the distance run.

Suppose that an object travels from one point in space to another. Make a comparison between the magnitude of the displacement and the distance traveled by this object.

• The displacement is always equal to the distance traveled.

• The displacement can be either greater than, smaller than, or equal to the distance traveled.

• The displacement is either less than or equal to the distance traveled.

• The displacement is either greater than or equal to the distance traveled.

Answer explanation

Displacement measures the shortest path between two points, while distance accounts for the actual path taken. Therefore, displacement is always less than or equal to the distance traveled.

When is the average velocity of an object equal to the instantaneous velocity?

• only when the velocity is decreasing at a constant rate

• always

• only when the velocity is increasing at a constant rate

• never

• when the velocity is constant

Answer explanation

The average velocity equals the instantaneous velocity when the velocity is constant. In this case, there is no change in speed or direction, making both velocities identical.

If the velocity of an object is zero at some point, then its acceleration must also be zero at that point.

• True

• False

Answer explanation

The statement is false. An object can have zero velocity while still experiencing acceleration, such as when it is at the peak of its motion (e.g., a ball thrown upwards). Thus, zero velocity does not imply zero acceleration.

Suppose that a car traveling to the west begins to slow down as it approaches a traffic light. Which of the following statements about its acceleration is correct?

• The acceleration is toward the west.

• The acceleration is toward the east.

• The acceleration is zero.

• Since the car is slowing down, its acceleration must be negative.

Answer explanation

As the car slows down while moving west, its acceleration is directed opposite to its velocity. Therefore, the acceleration is toward the east, indicating a decrease in speed.

Tags

NGSS.HS-PS2-1

An auto manufacturer advertises that their car can go "from zero to sixty in eight seconds." This is a description of what characteristic of the car's motion?

• instantaneous acceleration

• displacement

• instantaneous speed

• average speed

• average acceleration

Answer explanation

The phrase "from zero to sixty in eight seconds" indicates how quickly the car accelerates over that time, which defines its average acceleration, not instantaneous speed or other characteristics.

Under what condition is average velocity equal to the average of the object's initial and final velocity?

• This can only occur if there is no acceleration.

• The acceleration must be constantly decreasing.

• This can occur only when the velocity is zero.

• The acceleration must be constantly increasing.

• The acceleration is constant.

Answer explanation

Average velocity equals the average of initial and final velocity when acceleration is constant. This is because constant acceleration leads to a linear change in velocity, allowing the average to be simply the midpoint of the two velocities.

When a ball is thrown straight up with no air resistance, the acceleration at its highest point

• is zero

• reverses from downward to upward

• is downward

• reverses from upward to downward

• is upward

Answer explanation

At the highest point, the ball momentarily stops, but gravity still acts on it, causing a downward acceleration. Therefore, the correct answer is that the acceleration is downward.

Tags

NGSS.HS-PS2-1

A ball is thrown straight up, reaches a maximum height, then falls to its initial height. Which of the following statements about the direction of the velocity and acceleration of the ball as it is going up is correct?

• Its velocity points downward and its acceleration points upward.

• Both its velocity and its acceleration points downward.

• Both its velocity and its acceleration point upward.

• Its velocity points upward and its acceleration points downward.

Answer explanation

As the ball goes up, its velocity is directed upward due to its motion. However, the acceleration due to gravity always acts downward, opposing the motion. Thus, the correct statement is that its velocity points upward and its acceleration points downward.

Tags

NGSS.HS-PS2-1

A 10-kg rock and a 20-kg rock are thrown upward with the same initial speed v₀ and experience no significant air resistance. If the 10-kg rock reaches a maximum height h, what maximum height will the 20-kg ball reach?

• 4h

• h

• 2h

• h/2

• h/4

Answer explanation

The maximum height reached by an object thrown upward depends only on its initial speed and the acceleration due to gravity, not its mass. Therefore, the 20-kg rock will also reach the same maximum height h as the 10-kg rock.

Tags

NGSS.HS-PS2-4