Question

A stone is shot straight upward with a speed of 20 m/sec from a tower 200 m high. The speed with which it strikes the ground is approximately

• A. 60 m/sec
• B. 65 m/sec
• C. 70 m/sec
• D. 75 m/sec

Answer 1

Answer: (B)

65 m/sec

Answer 2

Speed of stone in a vertically upward direction is 20 m/s. So for vertical downward motion we will consider $u = - 20m/s$

$v^{2} = u^{2} + 2gh = ( - 20)^{2} + 2 \times 10 \times 200 \Rightarrow v = 65m/s$