An astronaut in space cannot use a scale or balance to weigh objects because the

Question

An astronaut in space cannot use a scale or balance to weigh objects because there is no gravity. But she does have devices to measure distance and time accurately. She knows her own mass is 87.2 kg, but she is unsure of the mass of a large gas canister in the airless rocket. When this canister is approaching her at 3.80m/s, she pushes against it, which slows it down to 1.20m/s (but does not reverse it) and gives her a speed of 2.00m/s.
A: What is the mass of this canister?
B: How much kinetic energy is

Explanation / Answer

the first part is a conservation of momentum problem momentum before collision = momentum after collision before, momentum = 3.2 m where m is the mass of the cannister after, momentum = 1 m + 2.5 * 89.7 kgm/s (the first term is the momentum of the cannister after collision, the second the momentum of the astronaut) therefore 3.2 m = 1 m + 224.25 => m=101.9kg KE before = 1/2 m v^2 = 1/2 *101.9kg x(3.2m/s)^2 = 521.9J KE after = 1/2*101.9 kg x (1m/s)^2 + 1/2*89.7kg x (2.5m/s)^2 = 331.3J subtract the two to find the energy lost

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