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#1 2007-02-22 06:03:36

StickInMaths
Guest

Constant acceleration

For some reason am not getting this

A, B and C are three points on a straight road such that AB=80 and BC=60. A car travelling with uniform acceleration passes A, B and C at times t=0s, t=4s and t=6s respectively. Modelling the car as a particle, find its acceleration and its velocity at A

#2 2007-02-22 07:24:14

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Constant acceleration

Heh, I recognise that exact question from when I did A-level mechanics about 2 years ago. I also remember having trouble with it. roll

You need to use s = ut+1/2at² for this. (u is initial velocity, a is acceleration)
You are told that it moves 80 metres in 4 seconds and that it moves 140 metres in 6 seconds.
Plugging those values into the kinematic equation gives you two simultaneous equations:

80 = 4u + 1/2a*4² = 4u + 8a
140 = 6u + 1/2a*6² = 6u + 18a

Now you have two unknowns and two equations, so it's just a matter of solving to find u and a.


Why did the vector cross the road?
It wanted to be normal.

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