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How to find the total momentum before and after a collision?

How to find the momentum before and after a collision?

  • A car (m=2000 kg) travelling at 20 m/s hits a deer (m=300 kg) standing still in the middle of the road. If the driver does not hit his brakes and the deer land on the hood of the car and stays on the hood, how fast does the car/deer object travel (v1) after the collision? PART 2: What is the momentum of the car (pc) and the deer (pd) before the collision, and the momentum of both (pb) after the collision? Please, i really need help! Thank you!! :D

  • Answer:

    Part 1 and Part 2 can be answered at the same time using the conservation of momentum. pi=pf pc+pd=pb (b-both) mc*vc + md*vd=mb*vb (knowing that velocity of the dear is 0 simplifies) mc*vc=mb*vb vb=(mc*vc)/mb vb=(2000*20)/(2000+300) vb=17.4m/s To find the momentum of each just substitute the known values and solve for momentum: pc=mc*vc pc=2000*20 pc=40 000 kg m/s pd=md*vd pd=300*0 pd=0 pb=mb*vb pb=2300*17.4 pb=40 000 kg m/s (should be equal to initial momentum of car and it is)

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Momentum is conserved in collisions. So the initial momentum is 2000*20 + 300*0 = 40,000 kg.m/s It must be the same after, so the velocity is 40000/(2000+300) =~ 17.4m/s If the car did hit the brakes, some momentum would be transferred to the Earth, but it's too small to measure the velocity difference :-)

adaviel

Momentum is conserved in collisions. So the initial momentum is 2000*20 + 300*0 = 40,000 kg.m/s It must be the same after, so the velocity is 40000/(2000+300) =~ 17.4m/s If the car did hit the brakes, some momentum would be transferred to the Earth, but it's too small to measure the velocity difference :-)

adaviel

Part 1 and Part 2 can be answered at the same time using the conservation of momentum. pi=pf pc+pd=pb (b-both) mc*vc + md*vd=mb*vb (knowing that velocity of the dear is 0 simplifies) mc*vc=mb*vb vb=(mc*vc)/mb vb=(2000*20)/(2000+300) vb=17.4m/s To find the momentum of each just substitute the known values and solve for momentum: pc=mc*vc pc=2000*20 pc=40 000 kg m/s pd=md*vd pd=300*0 pd=0 pb=mb*vb pb=2300*17.4 pb=40 000 kg m/s (should be equal to initial momentum of car and it is)

Akbar Shabaz

P is the same before & after: All the initial momentum comes from the car; the deer ha none-- Pdi = 0 Pci = mc*vc = 2000*20 = 40000 kg∙m/s Pb = Pci = (mc + md)*v1 → v1 = 40000/2300 = 17.39 m/s

Steve

P is the same before & after: All the initial momentum comes from the car; the deer ha none-- Pdi = 0 Pci = mc*vc = 2000*20 = 40000 kg∙m/s Pb = Pci = (mc + md)*v1 → v1 = 40000/2300 = 17.39 m/s

Steve

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