Hard

Question

One stone is projected horizontally from a 20 m high cliff with an initial speed of 10 ms-1. A second stone is simultaneously dropped from that cliff. Which of the following is true?

Options

A.Both strike the ground with the same speed.
B.The ball with initial speed 10 ms-1 reaches the ground first.
C.Both the balls hit the ground at the same time.
D.Both strike the ground with different speed

Solution

10 m/s = uA ;    uB = 0 m/s    uA = 10
On reaching the ground,
Both will have same vertical velocity   
Vy2 = uy2 + 2ay sy
since   uy =  0 for both A & B 
            ay = g  for both A & B      
            sy = 20 m for both A & B 
Thats why the time taken by both are same   

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