(a) Let the east be the positive direction. Then, according to the law of conservation of momentum, we have:
m1v1−m2v2=(m1+m2)vf,vf=(m1+m2)m1v1−m2v2,vf=(900 kg+1500 kg)900 kg⋅26 sm−1500 kg⋅30 sm=−9 sm.The sign minus means that the couple of the car and truck moves to the west.
(b) Let's find the average net force of each vehicle after the collision:
FavgΔt=m∣(vf−vi)∣,Favg=Δtm∣(vf−vi)∣,Favg,car=0.4 s900 kg⋅∣(−9 sm−26 sm)∣=78750 N,Favg,truck=0.4 s1500 kg⋅∣(−9 sm−30 sm)∣=146250 N.
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