1. In the movie Wall-E there is a mostly accurate scene where the robot Wall-E u

Question

1. In the movie Wall-E there is a mostly accurate scene where the robot Wall-E uses a fire extinguisher to maneuver around in space. You can see the scene at https //youtu.be/P8sUVhR7xjE. An average dry chemical fire extinguisher has 4 kg of chemicals that can be sprayed and the spray comes out of the nozzle at about 30 m/s. If we assume that the spray comes out ery quickly (so that we don't waste any momentum speeding up the spray before it get's sprayed out) and Wall-E has a mass of 10 kg, what is the top speed Wall-E could achieve using only a fire extinguisher?

Explanation / Answer

Applying conservation of momentum we have

initial momentum = final momentum

initially both walle and extinguisher are at rest so initial momentum is zero

0 = mv1 + Mv2

0 = 4(30) + 10v2

10v2? = -120

v2 = -12 m/s

The top speed achieved by wall e is 12 m/s

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