Car 1 of mass 700 kg is slowly moving along at 0.500 m/s when it is hit from beh

Question

Car 1 of mass 700 kg is slowly moving along at 0.500 m/s when it is hit from behind by car 2 speeding along at 15.0 m/s. After collision, car 1 has a new speed of 8.00 m/s in the same direction. Which of the following is the force with which car 2 must have struck car 1, if the collision lasted for 0.932 s? Also, knowing that conservation of momentum applies to the situation, what is car 2’s speed after the collision (v2f) if it has a mass of 850 kg? Select one: a. F = 5.63 × 103 N v2f = 8.82 m/s b. F = 5.64 × 103 N v2f = 5.89 m/s c. F = 5.64 × 103 N v2f = 8.82 m/s d. F = 5.63 × 103 N v2f = 7.50 m/s

Explanation / Answer

a). F = 5.63 × 103 N v2f = 8.82 m/s

Impulse = change in momentum

F.t = P

Impulse = 700kg*(8.00 - 0.50) m/s = 5250 N.s

So the force is 5250 N.s / 0.932s = 5.633*10^3 N

Total momentum P = (700*0.5) + (850*15.0) = 13100 kg.m/s

so momentum of car 2 after collision = 13100 - (700*8.00) = 7500 kg.m/s

so speed of car 2 = 7500kg.m/s / 850kg = 8.82 m/s

Looks like choice a. <= ANS

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