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# M2- Circular motion with variable speed watch

1. Q. A car is travelling on a horizontal road which is an arc of a circle with radius 400m. The car is travelling at a speed of 30ms-1 when the brakes are applied so that the speed decreases at a rate of 1ms-2. Find the total acceleration of the car.

a) immediately after the brakes have been applied
b) 5s later

A.
I've done part A. Here's my working...

tangential acceleration = -1
radial " " = v2/r = 30^2/400 = 2.25

sqrt(-1^2 + 2.25^2) = 2.46ms-2

How do I go about with B?
2. Find its speed after 5 seconds, then plug that into the equation

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Updated: October 12, 2006
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