fisica1-youn-e-freedman-exercicios-resolvidos

8.85: a) If the crate had final speed v , J&J have speed 4.00 m s − v relative to the ice,
(120.0 kg) (4.00 m s)
and so ( 15.0 kg) v = (120.0 kg)(4.00 m/s − v).
Solving for v v =
= 3.56m s.
,
(135.0 kg)
(75.0 kg)
b) After Jack jumps, the speed of the crate is (4.00m s) = 2.222m s,
and the
(135.0 kg)
momentum of Jill and the crate is 133.3 kg ⋅ m s . After Jill jumps, the crate has a speed v
and Jill has speed 4.00 m s − v,
and so
133 .3 kg ⋅ m s = (15.0 kg) v − ( 45.0 kg)(4.00 m s − v),
and solving for v gives
v = 5.22 m s. c) Repeating the calculation for part (b) with Jill jumping first gives a final
speed of 4 .67 m s.