Physics word problem.PLEASE HELP !!!!!!?

Question

A 2220 kg car traveling at 11.9 m/s collides with a 2670 kg car that is initially at rest at the stoplight. The cars stick together and move 2.40 m before friction causes them to stop. Determine the coefficient of kinetic friction between the cars and the road, assuming that the negative acceleration is constant and that all wheels on both cars lock at the time of impact.

Answer 1

Start with conservation of momentum


2220*11.9=(2220+2670)*v
v=5.40 m/s of the combined mass

now use conservation of energy to find the force of friction

.5*(2220+2670)*5.4^2=f*2.40
f=29700 N

f=N*µk

N=m*g
µk=29700/((2220+2670)*9.81)
µk=0.619

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