In a shotput event an athlete throws the shotput of mass 20 kg with an initial speed of `2 m s^(-1)` at `45^@` from height 3 m above ground. Assuming air resistance to be negligible and acceleration due to gravity to be `10 m s^(-2)`, the kinetic energy of the shotput when it just reaches the ground will be

Options

A. 2.5 J
B. 5.0 J
C. 52.5 J
D. 155.0 J

Answer

D

Explanation

Initial KE of the shotput
`=1/2(10 kg) (1 m//s^2)=5 J`
Initial PE of the shotput at a height 1.5 m above ground
`=mgh = (10 kg) (10 m//s^2) (1.5 m)=150 J`
Total initial energy of the shotput = 155 J
Since air resistance is negligible and final potential of the shotput as it hits the ground (h= 0) is zero, kinetic energy of the shotput on hitting the ground =155 J