Question

A tennis player serves a tennis ball such that it is moving horizontally when it leaves the racquet. When the ball travels a horizontal distance of 11 m, it has dropped 53 cmfrom its original height when it left the racquet. What was the initial speed, in m/s, of the tennis ball? (Neglect air resistance.)

  

Answer 1

horizontal distnace travelled by ball = d = 11 m

vertical distnace travelled in same time duration = h = 53 cm = 0.53 m

acceleration due to gravity = g = 9.8 m/s2

Let time taken to travel the above mentioned distances be t

in vertical direction, initial velocity is zero since the ball was travelling horizonatlly

initial vertical velocity = u = 0

h = u*t + 0.5*g*t2

0.53 = 0*t + 0.5*9.8*t2

t = 0.329 second

Horizontal distance travelled in this time = d = 11 m

Horizontal speed =horizontal distnace/time = 11/0.329 = 33.45 m/s

Since the ball was travelling horizontally initial, the vertical component of velocity is zero

Therefore initial speed of ball = horizontal speed = 33.45 m/s