(6) Wagon B is at rest so it has no momentum at the start. If v is the velocity of the wagons locked together, then
(140 kg) (15 m/s) = (140 kg + 200 kg) v
==> v ≈ 6.2 m/s
(7) False. If you double the time it takes to perform the same amount of work, then you halve the power output:
E / (2t ) = 1/2 × E/t = 1/2 P
