energy lost due to collision

2008-03-02 9:31 pm

個問題分3部份,我不懂c part

(Figure 8只是一張一架van 車尾損毀的相)
Figure 8 shows the damage of a van when it is hit by a fast moving car at the back. The masses of the van and the car are 150 kg and 80 kg respectively. It was found that, before the accident, the van and the car were moving with 25 m s-1 and 30 m s-1 respectively along the same straight road.

(a)Calculate the velocity of the van after the collision if that of the car is 24 m s-1. (2 marks)

(b)Justify any assumption you have made in answering (a).(2 marks)

(c)Calculate the energy lost due to the collision using your answer in (a).(2 marks)

回答 (1)

STEVIE-G™

2008-03-02 11:13 pm

✔ 最佳答案

(a)
Using conservatio n of momentum and let one side be positive
m1u+m2v=m1u'+m2v'
(150)(25)+(80)(30)=80(24)+(150)v
150v+1920=6150
v=28.2ms-1(along the original direction)
(b)
Assume there's no external force acting during the collision
(c)
The initial energy=(1/2)[150(25)2+(80)(30)2]=82875J
The final energy=(1/2)[150(28.2)2+(80)(24)2]=82683J
the energy lost due to the collision
=82875J-82683J
=192J

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