A child throws a ball with an initial speed of 8.00 m/s at an angle of 40.0° above the horizontal. The ball leaves her hand 1.00 m above the ground. How long is the ball in flight before it hits the ground?
A) 1.22 s
B) 6.79 s
C) 7.45 s
D) 9.14 s
E) 2.44 s

Question

Quizplus · Accepted Answer

We can use the kinematic equations to solve for the time the ball is in the air. Since we know the initial velocity of the ball, we can use the y-component of the velocity to find how long it takes for the ball to reach its maximum height.

vy = voy + at 
0 = 8.00 sin(40.0) - 9.81t 
t = 1.22 s

Since the time to reach the maximum height is the same as the time to fall back to the ground, the total time the ball is in the air is twice as long:

t_total = 2t 
t_total = 2 x 1.22 
t_total = 2.44 s

Therefore, the answer is A) 1.22 s.

A Child Throws a Ball with an Initial Speed of 8.00