Q#25
An object of mass m travelling with speed v has a head-on collision with another object of mass m travelling with speed v in the opposite direction. The two objects stick together after the collision.
What is the total loss of kinetic energy in the collision?
A 0 B ½ mv2 C mv2 D 2mv2
Solution:
Answer: C.
Momentum is a vector quantity and we need to consider the direction.
Since the objects are moving in opposite direction, one of them will have a negative value.
Sum of momentum before collision = mv – mv = 0
Kinetic energy is a scalar quantity and so, the direction of motion does not matter.
Sum of KE before collision = ½ mv2 + ½ mv2 = mv2
Momentum is always conserved.
Sum of momentum after collision = Sum of momentum before collision = 0
Sum of momentum after collision = 0
2mvf = 0
Giving the speed after collision, vf = 0
That is, the objects do not move after the collision.
KE after collision = 0
Loss in KE = mv2 – 0 = mv2
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