Physics Exam 2 Numbers 11-15

1. 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 acceleration due to gravity. The height from which they are dropped does not affect the time it takes for them to reach the ground. Therefore, statement I is true. Statements II and III are false because they suggest that one ball will reach the ground before the other, which is not the case.

Explanation

Both balls will strike the ground at the same time because they are both subject to the same acceleration due to gravity. The height from which they are dropped does not affect the time it takes for them to reach the ground. Therefore, statement I is true. Statements II and III are false because they suggest that one ball will reach the ground before the other, which is not the case.

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

A. parabola

B. arc

C. polygon

D. semicircle

The path of a projectile in the absence of air resistance is a parabola because the only force acting on the projectile is gravity. Gravity causes the projectile to follow a curved path, and the shape of this curve is a parabola. This can be explained by the fact that the vertical component of the projectile's velocity changes due to the acceleration caused by gravity, while the horizontal component remains constant. As a result, the projectile follows a curved trajectory that is described by a parabolic shape.

Explanation

The path of a projectile in the absence of air resistance is a parabola because the only force acting on the projectile is gravity. Gravity causes the projectile to follow a curved path, and the shape of this curve is a parabola. This can be explained by the fact that the vertical component of the projectile's velocity changes due to the acceleration caused by gravity, while the horizontal component remains constant. As a result, the projectile follows a curved trajectory that is described by a parabolic shape.

3. 15. Ignoring air resistance, the horizontal component of a projectile's motion is ___.

A. constant

B. accelerated

C. increasing

D. decreasing

The horizontal component of a projectile's motion is constant because there is no force acting on it in the horizontal direction. The only force acting on a projectile in the horizontal direction is its initial velocity, which remains constant throughout its motion. Therefore, the horizontal component of the projectile's motion does not change.

Explanation

The horizontal component of a projectile's motion is constant because there is no force acting on it in the horizontal direction. The only force acting on a projectile in the horizontal direction is its initial velocity, which remains constant throughout its motion. Therefore, the horizontal component of the projectile's motion does not change.

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 vx = constant and ay = -g. This means that the horizontal velocity of the projectile remains constant throughout its motion, while the vertical acceleration is equal to the acceleration due to gravity (-g). This is because in free fall, the only force acting on the projectile is gravity, which causes it to accelerate vertically downwards. The horizontal velocity, on the other hand, remains constant because there is no force acting in the horizontal direction.

Explanation

The motion of a projectile in free fall is characterized by vx = constant and ay = -g. This means that the horizontal velocity of the projectile remains constant throughout its motion, while the vertical acceleration is equal to the acceleration due to gravity (-g). This is because in free fall, the only force acting on the projectile is gravity, which causes it to accelerate vertically downwards. The horizontal velocity, on the other hand, remains constant because there is no force acting in the horizontal direction.

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.

To be considered a projectile, an object must be in free fall, meaning it is only affected by gravity and no other forces. The initial velocity of the object can have both vertical and horizontal components, but it must have a horizontal component in order to be considered a projectile. This is because a projectile follows a curved path, and the horizontal component of its initial velocity determines the range or distance it will travel horizontally. Without a horizontal component, the object would simply fall straight down without any horizontal displacement.

Explanation

To be considered a projectile, an object must be in free fall, meaning it is only affected by gravity and no other forces. The initial velocity of the object can have both vertical and horizontal components, but it must have a horizontal component in order to be considered a projectile. This is because a projectile follows a curved path, and the horizontal component of its initial velocity determines the range or distance it will travel horizontally. Without a horizontal component, the object would simply fall straight down without any horizontal displacement.