Question

Q1.
How much time will it take a a winch motor with a POWER of 10 horsepower to lift a 1300 kg crate straight up against gravity a distance of 10. (Conversion factor: 1 horsepower = 1 hp = 746 W)

Q2.
A ball with mass of 7.7 kg moving at 8 m/s collides elastically with a second ball that is initially stationary. If the second ball moves away at 2 after the collision, find the mass of the second ball.

Q3.
A 95 kg cyclist rolls down a hill that is 18 m high, starting at v = 2 m/s, and is travelling at 12 m/s at the bottom. Find the work done by friction/air resistance that slows her down.

Thanks!

Answer 1

So what is holding you back? Where are you getting stuck?
1. work in = force * distance moved in direction of force
power in = work in/time

2. first law. no change in total momentum
then
elastic collision means kinetic energy after = kinetic energy before

3. How much did potential energy m g h change ?
How much did kinetic energy (1/2) m v^2 change?
if some of the loss in potential energy did not result in kinetic energy, some got lost to friction

Answer 2

1. Po = 10*746 = 7460 Watts = 7460 Joules/s.
Work = F*d = Mg*d = 1300*9.8*10 = 127,400 J.
T = 127,400J. * 1s/7460J = ---S.