# E1t9 Preap Physics Numbers 21-25 2016

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• 1.

### 21. A baseball catcher throws a ball vertically upward and catches it in the same spot as it returns to the mitt. At what point in the ball’s path does it experience zero velocity and nonzero acceleration at the same time?

• A.

a. midway on the way up

• B.

b. at the top of its path

• C.

c. the instant it leaves the catcher’s hand

• D.

d. the instant before it arrives in the catcher’s mitt

B. b. at the top of its path
Explanation
At the top of its path, the ball experiences zero velocity because it momentarily stops moving before changing direction and starts moving downward. However, it still experiences nonzero acceleration because gravity is acting on it, pulling it downward.

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• 2.

### 22. Acceleration due to gravity is also called

• A.

A.negative velocity.

• B.

B. free-fall acceleration.

• C.

C.displacement.

• D.

D.instantaneous velocity.

B. B. free-fall acceleration.
Explanation
Acceleration due to gravity is also known as free-fall acceleration because it refers to the rate at which an object falls under the influence of gravity alone, without any other forces acting on it. This term is used to describe the constant acceleration experienced by objects in free fall, such as when an object is dropped from a height or when a projectile is launched vertically upwards and then falls back down. The acceleration due to gravity is approximately 9.8 m/s² on Earth.

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• 3.

### 23. Objects that are falling toward Earth in free fall move

• A.

A.faster and faster.

• B.

B. at a constant velocity.

• C.

C. slower and slower.

• D.

D.slower then faster.

A. A.faster and faster.
Explanation
When objects are falling toward Earth in free fall, they are under the influence of gravity. Gravity causes objects to accelerate, meaning their velocity increases over time. As the object falls, it experiences a constant force pulling it downward, causing it to speed up. Therefore, the correct answer is that objects falling toward Earth in free fall move faster and faster.

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• 4.

### 24. An object in free fall

• A.

A.experiences no air resistance.

• B.

B.undergoes a downward acceleration.

• C.

C.has an acceleration with a magnitude of 9.81 m/s2 near Earth’s surface.

• D.

D.all of the above

D. D.all of the above
Explanation
An object in free fall experiences no air resistance because there is no force opposing its motion. It undergoes a downward acceleration because gravity is acting on it, pulling it towards the Earth. This acceleration has a magnitude of 9.81 m/s2 near Earth's surface, as determined by the acceleration due to gravity. Therefore, all of the statements (a, b, and c) are correct.

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• 5.

### 25. When there is no air resistance, objects of different masses dropped from rest

• A.

A.fall with equal accelerations and with equal displacements.

• B.

B.fall with different accelerations and with different displacements.

• C.

C.fall with equal accelerations and with different displacements.

• D.

D.fall with different accelerations and with equal displacements.

A. A.fall with equal accelerations and with equal displacements.
Explanation
When there is no air resistance, objects of different masses dropped from rest will fall with equal accelerations and with equal displacements. This is because in the absence of air resistance, the only force acting on the objects is gravity, which is the same for all objects regardless of their mass. Therefore, all objects will experience the same acceleration due to gravity and will fall with the same rate. Additionally, since the objects are dropped from rest, they all start at the same initial position and therefore will have the same displacement at any given time.

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