JEE Main Physics question

A boy standing at the top of a tower of 20 m height drops a stone. Assuming ms, the velocity with which it hits the ground is [CBSE PMT (Prelims) 2011]

• (A)10.0 m/s
• (B)5.0 m/s
• (C)40.0 m/s
• (D)20.0 m/sCorrect