Physic 求救!!!

2008-05-14 2:51 pm

A truck P of 5500kg was park on the first lane.
Anthor truck Q of 3000kg hit into truck P and both trucks move forward for
30m after collision.
(The friction acting on the trucks is 6000N when they moved together.)

a)What was the speed of thr trucks after collision?
b)if the time of collision was 0.05s, what was the force acting on truck P?
c)What was the force acting on truck Q?
d)Find the speed of truck Q before collision.

請列式計算。

回答 (1)

Audrey Hepburn

2008-05-14 3:26 pm

✔ 最佳答案

a. By Newton’s 2ndlaw of motion,
F = ma
-6000 = (5500 + 3000)a
Acceleration, a = -12/17ms-2
By v2 = u2+ 2as
02 = u2+ 2(-12/17)(30)
Speed after collision, u= 6.51 ms-1

b. By impulse = changeof momentum
Ft = mv – mu
F(0.05) = (5500)(6.51 -0)
Force acting on P, F =7.16 X 105 N

c. By Newton’s 3rd law of motion, the forceacting on P and Q are action and reaction pairs. They are equal in magnitudebut opposite in direction.
Therefore, forceacting on Q is 7.16 X 105 N

d. By the law ofconservation of momentum
Initial momentum =Final momentum
mau = (ma+ mb)v
3000u = (3000 + 5500)(6.51)
Speed of Q beforecollision, u = 18.4 ms-1

參考: Myself~~~

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