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 75.9kg , but she is unsure of the mass of a large gas canister in the airless rocket. When this canister is approaching her at 3.40m/s , she pushes against it, which slows it down to 1.30m/s(but does not reverse it) and gives her a speed of 2.10m/s .

What is the mass of this canister?

How much kinetic energy is

Explanation / Answer

a)
use conservation of momentum:
initial momentum=final momentum
m*3.4=m*1.3+75.9*2.1
2.1 m =159.39
m=75.9 Kg

mass of canister is 75.9 kg

b)
loss in Kinetic energy= final K.E - initial K.E
                            =(0.5*75.9*2.1^2 + 0.5*75.9*1.3^2) - 0.5*75.9*3.4^2
                     =157.5 J

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