position and movement

Larry

2009-10-12 6:20 am

A car undergoes uniform decleration along a straight road,Its velocity decreases from 30ms^-1 after travelling a distance of 100m.How much further will the car travel before it comes to a rest?
A.50m
B.80m
C.180m
D.200m
E.300m
列算式thx

回答 (1)

Prof. Physics

2009-10-12 5:37 pm

✔ 最佳答案

You have some information missing. How much does its velocity decrease?

As far as I remember this question, the velocity should decrease from 30 m/s to 20 m/s in 100 m.

So, I will use this to do the question.

Initial velocity, u = 30 m/s

Final velocity, v = 20 m/s

Distance, s = 100 m

By v2 = u2 - 2as

(20)2 = (30)2 - 2a(100)

Deceleration, a = 2.5 ms-2

Now, initial velocity, u = 20 m/s

Final velocity, v = 0

By v2 = u2 - 2as

0 = (20)2 - 2(2.5)s

Further distance, s = 80 m

So, the answer is B.

參考: Physics king

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