In the railroad freight yard, an empty freight car of mass m rolls along a strai

Question

In the railroad freight yard, an empty freight car of mass m rolls along a straight level track at 1.0 m/s and collides with an initially stationary, fully loaded boxcar of mass 4.0m. The two cars couple together upon collision. (a) What is the speed of the two cars after the collision? Incorrect: Your answer is incorrect. m/s (b) Suppose instead that the two cars are at rest after the collision. With what speed was the loaded boxcar moving before the collision if the empty one was moving at 1.0 m/s? m/s

Explanation / Answer

part 1

m1=m

u1=4

u2=0

m2=4m

v=velocity after collision

according to conservation of linear momentum

m1.u1+m2.u2=m1.v1+m2.v2

m1.u1+m2.u2=(m1+m2 ).v

1.*m+0=(m+4m)v

v=(1*m) / (m+4m) m/s

v=1/5=0.2 m/s

part 2

the loaded boxcar was moving at a velocity of u before thecollision

final velocity =0 ie v1=0 and v2=0

u1=1

m1.u1+m2.u2=m1.v1+m2.v2

1*m+4m*u=0

u=-(1*m)/4m=0.25 m/s

the loaded boxcar was moving at avelocity of -(1*m)/4m=0.25 m/s

the negative sign suggest that the boxercar was moving towardsthe empty freight.

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