Quiz 2.4 Free Fall

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

• is upward

• is downward

• is zero

• reverses from upward to downward

A rock from a volcanic eruption is launched straight up into the air with no appreciable air resistance. Which one of the following statements about this rock while it is in the air is correct?

• On the way up, its velocity is upward, and at the highest point its velocity is zero.

• On the way down, its velocity is downward, and at the highest point its acceleration is zero.

• Throughout the motion, the velocity is always in the same direction as the acceleration.

• The acceleration is downward at all point in the motion except that is zero at the highest point.

A 10-kg rock and a 20-kg rock are dropped at the same time and experience no significant air resistance. If the 10-kg rock falls with acceleration a, what is the acceleration of the 20-kg rock?

• 4a

• 2a

• a

• a/2

Brick A is dropped from the top of a building. Brick B is thrown straight down from the same building, and neither one experiences appreciable air resistance. Which statement about their accelerations is correct?

• The acceleration of A is greater than the acceleration of B.

• The acceleration of B is greater than the acceleration of A.

• The two bricks have exactly the same acceleration.

• Neither brick has any acceleration once it is released.

A ball is thrown upward at a velocity of 19.6 m/s. What is its velocity after 3.0 s, assuming negligible air resistance?

• 9.8 m/s upward

• 9.8 m/s downward

• 0 m/s

• 19.6 m/s downward

In an anger attack, a person throws a cellphone downward from the top of a building with an initial speed of 25 m/s. It strikes the ground after 2.0 s. How high is the building, assuming negligible air resistance?

• 20 m

• 30 m

• 50 m

• 70 m