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Physics Sled momentum ?
A 33 kg child sleds down a hill and then coasts along the flat section at the bottom, where a second 33 kg child jumps on the sled as it passes by her. If the speed of the sled is 7.1 m/s before the second child jumps on, what is its speed (in m/s) after she jumps on? (Assume the mass of the sled is negligible and the second child's motion before landing on the sled is perfectly vertical.)
1 Answer
- AshLv 75 months ago
Kinetic energy of the sled with one child =½m₁v₁² = ½(33 kg)(7.1 m/s)² = 832 J
With 2nd child the KE stays the same, so we get
KE with 2 children = ½(m₁+m₂)v₂²
(832 J)= ½[(33 kg)+(33 kg)]v₂²
v₂² = 832/33
v₂ = 5.0 m/s ← speed of the sled after the 2nd child jumps in it
