A railway engine of mass 5000kg travels along a level track at 75 kmph and collides with a wagon of mass 15000 kg travelling in the opposite direction with a velocity of 20kmph. After impact the engine is found to travel in the same direction as before with the speed of 3kmph. Find the speed of the wagon.
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The final speed of the wagon = 4 Km/hr
m1 - mass of engine = 5000 kg
m2 - mass of the wagon = 15000 kg
v1 - initial velocity of engine = 75 Km/hr
v2 - initial velocity of wagon = 20 Km/hr
v1' - final velocity of engine = 3 Km/hr
v2' - final velocity of wagon
The initial velocity of the wagon will be taken as negative because it's velocity is in opposite to the direction of velocity of the engine
Initial momentum = m1v1 + m2v2
= 5000 × 75 + 15000 × (-20)
= 75000
Final momentum = m1v1' + m2v2'
= 5000 × 3 + 15000 × v2'
Using law of conservation of momentum-
Initial momentum = final momentum
=> 75000 = 15000 + 15000 v2'
=> v2' = 4 Km/hr
The final speed of the wagon = 4 Km/hr in the direction of the engine.
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