During the First World War, large cannons were mounted on railroad cars. A parti

Question

During the First World War, large cannons were mounted on railroad cars. A particular gun had a mass of 250,000 kg (including the railroad car) and fired 1500-kg shells with a muzzle velocity of 450 m/s at an angle of 20° above the horizontal.

A) If this cannon is fired form a stationary railroad car, find the recoil velocity of the gun + railraod car system right after firing the gun.

I got an answer of 2.54 m/s, but I'm not sure if this is right.

B) If the railroad car stops after 6.0 m after recoiling, find the work done against friction.

I got an answer of 806,450 J, but I'm not sure if this is right either.

C) When the gun is fired, 50% of the energy generated is in the form of heat. The other 50% of energy is in the form of mechanical energy. Find the total energy generated by firing the gun.

I have no idea where to even start with this one...

Explanation / Answer

A)

initial momentm Pi = 0

after firing

along horizontal

momentum conservation

Pf = Pi

M*V = m*ux

V = 1500*450*cos20/250000

V = 2.54 m/s

===================

(B)

work = change in KE = (1/2)*M*V^2 = (1/2)*250000*2.54^2 = 806450 J

===================

(C)

Mechanical energy KE = (1/2)*M*V^2 + (1/2)*m*u^2

KE = (0.5*250000*2.54^2) + (0.5*1500*450^2)

KE = 152681450 J

thermal enrgy Et = 152681450 J

total energy E = 152681450 + 152681450 = 305362900 J <<<<-------answer

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