Homework Help: 3 questions

1. Nov 29, 2006

dronegun

i am finding these hard. Any help appreciated

A 1.0 103 kg Rover collides into the rear end of a 2.2 103 kg BMW stopped at a red light. The bumpers lock, the brakes are locked, and the two cars skid forward 2.1 m before stopping. The police officer, knowing that the coefficient of kinetic friction between tires and road is 0.36, calculates the speed of the Rover at impact. What was that speed?

A 16 g rifle bullet traveling 235 m/s buries itself in a 3.1 kg pendulum hanging on a 2.8 m long string, which makes the pendulum swing upward in an arc. Determine the horizontal component of the pendulum's displacement.

A 0.200 kg croquet ball makes an elastic head-on collision with a second ball initially at rest. The second ball moves off with half the original speed of the first ball.
(a) What is the mass of the second ball?
kg
(b) What fraction of the original kinetic energy (KE/KE) gets transferred to the second ball?

2. Nov 29, 2006

AlephZero

You need to use two principles, conservation of momentum, and conservation of energy.

Remember momentum is conserved when the impact occurs, but energy is not.

For the first question, call the velocity before the impact V1 and after the impact V2. So you need two equations to find two unknowns. First equation: After the impact, the kinetic energy of the cars = the work done by friction of the tires. Second equation: During the impact, momentum is concerved.