A 39 kg girl runs across a mat with a speed of 4.8 m/s and jumps onto a 125 kg hanging platform initially at rest, causing the girl and platform to swing back and forth like a pendulum together after her jump. What is the combined velocity of the girl and platform (in m/s) after the jump?

The combined velocity of the girl and the platform after the jump is 1.14 m/s.

Explanation:

From the law of conservation of momentum:

m1u1 = (m1 + m2)v

m1 is mass of the girl = 39 kg

m2 is mass of the hanging platform = 125 kg

u1 is initial speed of the girl = 4.8 m/s

v is combined velocity of the girl and the platform after the jump

v = m1u1/(m1+m2) = 39×4.8/(39+125) = 187.2/164 = 1.14 m/s

its c i just checked it