addy899
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1. Two carts, each of mass M, travel towards each other on a frictionless air track, one with velocity V, and the other with -3V. They collide and stick together. How much kinetic energy is lost in the collision?
2. P = mv, KE=1/2mv2
3. Initial KE of the system is the sum of the kinetic energies of the two masses.
K1 = (1/2)Mv2, K2 = (1/2)m(-3v)2 = 9mv2
sum: 10mv2
assuming momentum is conserved, velocity of the two masses after the collision is -V.
Then calculate final KE = 1/2(2m)(-V)2 = mv2
subtract this from the initial and I get 9mv2 Joules are lost in the collision.
My key says the answer is 4mv2
2. P = mv, KE=1/2mv2
3. Initial KE of the system is the sum of the kinetic energies of the two masses.
K1 = (1/2)Mv2, K2 = (1/2)m(-3v)2 = 9mv2
sum: 10mv2
assuming momentum is conserved, velocity of the two masses after the collision is -V.
Then calculate final KE = 1/2(2m)(-V)2 = mv2
subtract this from the initial and I get 9mv2 Joules are lost in the collision.
My key says the answer is 4mv2