# Practice on Speed, Velovity, and Acceleration: Solution-2

Question 1: A ball is projected upward. Eventually, after the ball reaches its maximum height, it will fall back.
Indicate which statement is correct:
• speed never changes
• At the highest point in its motion, the ball's velocity is zero.
• At the highest point in its motion, the ball's velocity is not zero
• none of the above
At the highest point in its motion, the ball's velocity is zero.

Question 2: Assume a student throws a ball vertically downward with a velocity of 10 m/s.
If air friction is considered negligable then calculate the speed of the ball one second later.
• 9.8 m/s
• 20 m/s
• 19.8 m/s
• 18.8 m/s
Answer: assuming that g = 9.8 m/s2 then speed of the ball 1 second later = 19.8 m/s

Question 3: Suppose you throw a ball vertically with a velocity of 10 m/s.
Approximately, when will it reach its highest height?
• 3 s.
• 2 s.
• 5 s.
• 1 s.
Answer: In 1 s. After 1 second, the gravity will push it down.

Question 4: Assume a television screen fall down from rest at a great height.
Calculate the speed after it has fallen for 5 seconds where air resistance is considered negligible.
• 49 m/s
• 48 m/s
• 47m/s
• 46m/s
Explanation: acceleration (a) = speed (v) divided by elapased time (t), which implies that v = a × t = 9.8 m/s2 × 5 s = 49 m/s

Question 5: Assume a box of 5 kg is dropped from a building and hits the ground in 7 s.
Calculate the time it takes for a 10-kg box to hit the ground where air resistance is considered negligible.
• 14 s
• 10 s
• 5 s
• 7 s

Explanation: since air resistance is zero then the time would stay the same.

Question 6: If a rocket is fired from a fighter jet and assuming that air resistance is negligible.
Which statement is correct about the rocket.
• The rocket stops immediately.
• Its speed doubles every second.
• Its speed increases at 9.8 m/s.
• none of the above.
Answer: Its speed increases at 9.8 m/s.

Question 7: If you throw a ball up in the air.
Indicate the status of the ball when it reaches its highest point.
• acceleration is zero.
• speed doubles every second.
• velocity is halved and the acceleration is downward.
• velocity is zero and the acceleration is downward.
• none of the above.
Answer: velocity is zero and the acceleration is downward.

Question 8: If you throw a ball up in the air with an initial velocity of 20m/s.
Calculate the ball's velocity after 4 seconds.
• − 19.2 m/s
• 0 m/s
• 19.2 m/s
• 20 m/s