m = mass of the rock = 0.5 kg
v = velocity of the rock = 10 m/s
V = velocity of eli in opposite direction of the rock = - 0.05 m/s
M = mass of eli and skateboard together = ?
V' = velocity of combination of rock , skateboard and eli together before rock is thrown = 0 m/s
using conservation of momentum
total momentum after throwing rock = total momentum before throwing rock
mv + MV = (M + m) V'
(0.5) (10) + M (- 0.05) = (0.5 + M) (0)
M = 100 kg
