Question

A 60-kg swimmer suddenly dives horizontally from a 150-kg raft with a speed of 1.5 m/s. The raft is initially at rest. What is the speed of the raft immediately after the diver jumps if the water has negligible effect on the raft? site is giving all wrong answers it is not 0.6 m/s or -0.6 m/s

Answer 1

Using Momentum conservation:

Pi = Pf

Given that initially raft is at rest, So

Pi = 0

Which means Pf = 0

Pf = m1*V1 + m2*V2

m1*V1 + m2*V2 = 0

V2 = -m1*V1/m2

Given that

m1 = mass of swimmer = 60 kg

m2 = mass of raft = 150 kg

V1 = speed of swimmer = 1.5 m/sec

So,

V2 = -60*1.5/150

V2 = Velocity of raft = -0.60 m/sec (here -ve sign means direction of raft will be in opposite direction of swimmer)

|V2| = Speed of raft = |-0.60| = 0.60 m/sec

Answer should be 0.60 m/sec, either you should try 0.60 m/sec instead of 0.6 m/sec (because of significant figures) or try this value without the unit of m/sec, Let me know if any of this works, otherwise ask your instructor to check if there is any mistake in this question, as correct answer should be 0.60 m/sec