Spring Physics Exam 2 #'s 11-15

1. 11. In the absence of air resistance, the path of a projectile is a(n)

A. parabola

B. arc

C. polygon

D. semicircle

In the absence of air resistance, the path of a projectile follows a parabolic trajectory. This is because the only force acting on the projectile is gravity, which causes it to accelerate downwards. As a result, the projectile follows a curved path that is symmetric around its highest point. This curved path is known as a parabola, and it is the correct answer to this question.

Explanation

In the absence of air resistance, the path of a projectile follows a parabolic trajectory. This is because the only force acting on the projectile is gravity, which causes it to accelerate downwards. As a result, the projectile follows a curved path that is symmetric around its highest point. This curved path is known as a parabola, and it is the correct answer to this question.

2. 14. A baby drops a ball from her hand resting on the serving tray of her high chair. Simultaneously, she knocks another ball from the same tray. Which of the following statements are true? I. Both balls strike the ground at the same time.II. The dropped ball reaches the ground first.III. The knocked ball reaches the ground first.

A. I only

B. II only

C. III only

D. None are true

Both balls will strike the ground at the same time because they are both subject to the same gravitational force and have the same initial height. The fact that one ball was dropped and the other was knocked does not affect their acceleration due to gravity. Therefore, statement I is true. Statement II is false because the dropped ball and the knocked ball will reach the ground at the same time. Statement III is false for the same reason.

Explanation

Both balls will strike the ground at the same time because they are both subject to the same gravitational force and have the same initial height. The fact that one ball was dropped and the other was knocked does not affect their acceleration due to gravity. Therefore, statement I is true. Statement II is false because the dropped ball and the knocked ball will reach the ground at the same time. Statement III is false for the same reason.

3. 15. Which of the following is an example of projectile motion?

A. a jet lifting off a runway

B. a baseball being thrown

C. dropping an aluminum can into the recycling bin

D. a space shuttle orbiting Earth

An example of projectile motion is a baseball being thrown. Projectile motion refers to the motion of an object that is launched into the air and moves along a curved path under the influence of gravity. When a baseball is thrown, it follows a parabolic trajectory due to the initial force applied and the gravitational force acting on it. The baseball moves upward, reaches its highest point, and then falls back down to the ground following a curved path. This motion is characteristic of projectile motion.

Explanation

An example of projectile motion is a baseball being thrown. Projectile motion refers to the motion of an object that is launched into the air and moves along a curved path under the influence of gravity. When a baseball is thrown, it follows a parabolic trajectory due to the initial force applied and the gravitational force acting on it. The baseball moves upward, reaches its highest point, and then falls back down to the ground following a curved path. This motion is characteristic of projectile motion.

4. 12. The motion of a projectile in free fall is characterized by

A. ax = ay = -g.

B. ax = constant and vy = constant.

C. vx = constant and ay = g.

D. vx = constant and vy = constant.

The motion of a projectile in free fall is characterized by a constant horizontal velocity (vx = constant) and a vertical acceleration due to gravity (ay = -g). This means that the horizontal component of the projectile's velocity remains constant throughout its motion, while the vertical component experiences a constant downward acceleration due to gravity. Therefore, option c, vx = constant and ay = -g, accurately describes the motion of a projectile in free fall.

Explanation

The motion of a projectile in free fall is characterized by a constant horizontal velocity (vx = constant) and a vertical acceleration due to gravity (ay = -g). This means that the horizontal component of the projectile's velocity remains constant throughout its motion, while the vertical component experiences a constant downward acceleration due to gravity. Therefore, option c, vx = constant and ay = -g, accurately describes the motion of a projectile in free fall.

5. 13. For an object to be a projectile, it must be in free fall and its initial velocity must

A. have a horizontal component.

B. have both a vertical and a horizontal component.

C. have either a vertical or a horizontal component.

D. start from rest.

In order for an object to be a projectile, it must be in free fall, which means it is only under the influence of gravity. The initial velocity of the object must have a horizontal component because it is this horizontal component that allows the object to travel in a curved path. Without a horizontal component, the object would simply fall straight down. Therefore, option a. "have a horizontal component" is the correct answer.

Explanation

In order for an object to be a projectile, it must be in free fall, which means it is only under the influence of gravity. The initial velocity of the object must have a horizontal component because it is this horizontal component that allows the object to travel in a curved path. Without a horizontal component, the object would simply fall straight down. Therefore, option a. "have a horizontal component" is the correct answer.