A 50 kg boy jumps off the back of a 4 kg skateboard moving forward. Find the skateboard's velocity immediately after the boy jumps, assuming that the skateboard's initial velocity is 5 m/s and the boy's velocity when jumping off the back is 2.5 m/s in the forward direction.

M = mass of the boy = 50 kg

m = mass of the skateboard = 4 kg

V' = velocity of the combination of boy and skateboard before the jump = 5 m/s

v = velocity of the boy after jump = 2.5 m/s

V = velocity of the skateboard after jump = ?

using conservation of momentum

M V + m v = (M + m) V'

(50) V + (4) (2.5) = (50 + 4) (5)

(50) V + 10 = 270

50 V = 260

V = 260/50

V = 5.2 m/s