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# m1 help watch

1. m1 mechanics help

"in two consecutive seconds, a car travels through 20m and 15m respectively. The car is travelling with uniform deceleration."

i) find the speed of the car at the start of the 2 seconds and its deceleration.

Okay, i know it involes simultaneous equations but in the mark scheme they got the equations

by using , , and . I get this part.

But then they go on to do , ,, to get

okay , this is all good but why cant you take , , , to form the second equation, thanks
2. (Original post by upthegunners)
m1 mechanics help

"in two consecutive seconds, a car travels through 20m and 15m respectively. The car is travelling with uniform deceleration."

i) find the speed of the car at the start of the 2 seconds and its deceleration.

Okay, i know it involes simultaneous equations but in the mark scheme they got the equations

by using , , and . I get this part.

But then they go on to do , ,, to get

okay , this is all good but why cant you take , , , to form the second equation, thanks
The reason for that is that the initial velocity is different in each so it is no longer u in the second equation. The start velocity in the second equation you made is the final velocity of the first equation, therefore your equations are solving for a value of u that is different for each equation

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Updated: May 12, 2013
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