Physics 一問

Velocity of ball before striking the ground
= square-root[2g x 5] m/s = 10 m/s
where g is the acceleration due to gravity(=10 m/s2)
Since the ball rebound to the same height, by conservation of energy, velocity of ball after rebound = 10 m/s
using: impulse = change of momentum
F.(0.1) = 1 x (10-(-10))
where F is the net force acting on the ball
But F = (R-1xg), where R is the reaction force acting on the ball
hence, R - g = 1 x (20)
R = (20 + 10) N = 30 N