A boy is standing on top of a tower of height 85 m and throws a ball in the vertically upward direction with a certain speed. If `5.25` seconds later he hears the ball hitting the ground, then the speed with which the boy threw the ball is (take `g = 10 m/s^(2)`, speed of sound in air = 340 m/s)

Options

A. 6 m/s
B. 8 m/s
C. 10 m/s
D. 12 m/s

Answer

B

Explanation

Time taken by sound `=(85)/(340)=0.25` sec
Time taken by ball = `5.25-0.25=5sec`
Now, `85=uxx5-(1)/(2)xx10xx25impliesu=8m//sec`.