A ball is thrown straight up with an initial speed of 30 m/s. What is its speed after 4.2 s?
A) 72 m/s
B) 42 m/s
C) 30 m/s
D) 11 m/s

Question

Quizplus · Accepted Answer

When a ball is thrown straight up, the only force acting on it is gravity, which pulls it downward. As the ball rises, its speed decreases until it reaches its maximum height at which point its speed is zero. Then, as it falls back down, its speed increases again. At the highest point, the acceleration due to gravity is equal to the initial upward velocity of the ball (which is 30 m/s in this case), so its speed after 4.2 s is equal to 30 m/s - (9.8 m/s^2 x 4.2 s) = 11 m/s.

A Ball Is Thrown Straight Up with an Initial Speed