Skateboarder A (80 kg) is going to the right at 10 m/s. Skateboarder B (50 kg) i

Question

Skateboarder A (80 kg) is going to the right at 10 m/s. Skateboarder B (50 kg) is going to the left at velocity v. They have a collision but manage to bounce off each other so that A is going to the left with a speed of 2 m/s and B is going to the right with a speed of 3 m/s. (a) What was B’s initial velocity? (b) How much energy was lost in the collision? Skateboarder A (80 kg) is going to the right at 10 m/s. Skateboarder B (50 kg) is going to the left at velocity v. They have a collision but manage to bounce off each other so that A is going to the left with a speed of 2 m/s and B is going to the right with a speed of 3 m/s. (a) What was B’s initial velocity? (b) How much energy was lost in the collision? Skateboarder A (80 kg) is going to the right at 10 m/s. Skateboarder B (50 kg) is going to the left at velocity v. They have a collision but manage to bounce off each other so that A is going to the left with a speed of 2 m/s and B is going to the right with a speed of 3 m/s. (a) What was B’s initial velocity? (b) How much energy was lost in the collision?

Explanation / Answer

from the conservation of momentum

m1u1+m2u2 = m1v1+m2v2

m2u2 = m1v1+m1v1-m1u1

50*u2 = -80*2+50*3-80*10

50 u2 = -160+150-800

u2 = -16.2 m/s

initial velocity of B is 16.2 m/s moving towards left direction

b) initial kinetic energy ki = 1/2*80*10^2+1/2*50*16.2^2 = 10561 J

kfinal = 1/2*80*2^2+1/2*50*3^2 = 160+225 = 385 J

loss in energy = 10561-385 = 10176 J

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