- #1

Nimrod 7

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## Homework Statement

A sprinter runs a race with constant acceleration throughout. During the race he passes four posts A, B, C, D in a straight line such that |AB| = |BC| = |CD| = 20m. If the sprinter takes 5 seconds to go from A to B and 3 seconds to go from B to C, find out how long, the the nearest tenth of a second, it takes him to run from C to D

## Homework Equations

s = (v + u)/2 x t

## The Attempt at a Solution

I have a way of doing it but it takes up almost 1 A4 page :( I did it this way and the answer was wrong, wasn't surprised cos there was loads of room for error

I did s = (v + u)/2 x t

substituted (v - at) instead of u (v = u + at, u = v-at)

And got v1 in terms of a

Then did s = (v + u)/2 x t

Substitued (u+at) instead of v

Got u2 in terms of a

v1 = u2 so I got the acceleration

I kept doing this to get the u and v for C to D and used the acceleration to calculate the time

But it was wrong

I know there's a shorter way of doing it

Can someone help me? Final answer is 2.4s (nearest tenth of a second)