Question

A boy sees a ball go up and then down through a window 2.45m high. If the total time that ball is in sight is 1s, the height above the window the ball rises is approximately a) 2.45m b) 4.9m c)0.3m d) 0.49m

Answer 1

s = u t - 1/2 g t²

u = speed when the ball passes the bottom of the window.
Time duration for traveling window height one way = 1/2 sec.

2.45 = u * 1/2 - 1/2 * 9.8 * 1/2²
=>   u = 7.35 m/s

Total height the ball rises from the bottom of the window 
   s1 = 7.35²/(2*9.8) = 2.75625 m

The height above the top edge of the window, the ball rises
    = 0.30625 m

ans  (c)

Answer 2

Answer:

Explanation: h from the ground to the window is 2.45 m

Time can be taken as 0.5 sec

H=ut-1/2gt ^2

2.45=u*0.5-1/2*9.8*0.5^2

By solving this equation we get u=7.35m/s .

By using the formula h max =u^2/2g,we get

7.35^2/2*9.8=2.756 m

So , the height above the window is equal to 2.756-2.45=0.306