A 40 kg girl who is running at 2.5 m/s jumps.....?

Question

A 40 kg girl who is running at 2.5 m/s jumps on a stationary 10 kg sled on a frozen lake. How fast do she and the sled then move?

Answer 1

Assuming that there is no friction the conservation of momentum will yield
m1u1=(m1+m2)V

V=u1 m1/(m1+m2)

V= 2.5 x 40/(40 + 10)=2.0m/s