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 very 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? 2. A bullet with a mass of 11 g leaves the barrel of a rifle with a velocity of 890 m/s. The rifle has a mass of 4.3 kg. Find the recoil velocity of the rifle after firing the bullet. Explain in words why getting hit by a rifle with that much momentum is fair less damaging than getting hit by a bullet with the same momentum.

Explanation / Answer

1)

let,

m1=4kg

v1=30 m/sec

and

m2=10 kg

by using law o conservation momentu,

m1*v1=m2*v2

4*30=10*v2

===> v2=12 m/sec

speed of the wall-E is, v2=12 m/sec

2)

let,

m1=11g=11*10^-3 kg

v1=890 m/sec

and

m2=4.3 kg

by using law o conservation momentu,

m1*v1=m2*v2

11*10^-3*890=4.3*v2

===> v2=2.277 m/sec

recoil velocoty of the rifle, v2=2.277 m/sec

here, speed of the bullet is greater than the recoil velocity of the rifle ,

hence, damage causes due to rifile is lesser than the bullet

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