A railroad car of mass 2.0 104 kg moving at 3.50 m/s collides and couples with two coupled railroad cars, each of the same mass as the single car and moving in the same direction at 1.20 m/s.
(a) What is the speed of the three coupled cars after the collision?
____________ m/s
(b) How much kinetic energy is lost in the collision?
_____________ J
(a) What is the speed of the three coupled cars after the collision?
____________ m/s
(b) How much kinetic energy is lost in the collision?
_____________ J
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Let m be the mass of 1 railroad car (it gives neater working)
Initial momentum = 3.50m + 2(1.20m)
Final momentum = (3m)v
SInce initial momentum, = final momentum,
3.50m + 2(1.20m) = (3m)v
3.5 + 2.4 = 3v
Notice m cancels - it doesn't affect the answer. Work out v.
Use KE = (1/2)mv^2 to work out each railroad car's kinetic energy before and after the collision.
KE lost = Initial KE - Final KE
Initial momentum = 3.50m + 2(1.20m)
Final momentum = (3m)v
SInce initial momentum, = final momentum,
3.50m + 2(1.20m) = (3m)v
3.5 + 2.4 = 3v
Notice m cancels - it doesn't affect the answer. Work out v.
Use KE = (1/2)mv^2 to work out each railroad car's kinetic energy before and after the collision.
KE lost = Initial KE - Final KE