- #1

life is maths

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## Homework Statement

Hi everyone! This is my homework question, an easy one, but I cannot find my mistake. Any help will be greatly appreciated.

Mary and Sally are in a foot race. When Mary is 22 m/s from the finish line, she has a speed of 4.0 m/s and is 5.0 m behind Sally, who has a speed of 5.0 m/s. During the remaining portion of the race, Sally decelerates at a constant rate of 0.48 m/s

^{2}to the finish line.

What constant acceleration does Mary now need during the remaining portion of the race, if she wishes to cross the finish line side-by-side with Sally?

## Homework Equations

## The Attempt at a Solution

(The final velocity of Sally)=V

_{sf}

^{2}

(The initial velocity of Sally)=V

_{si}

^{2}

V

_{sf}

^{2}:V

_{si}

^{2}-2ax

V

_{sf}

^{2}=5

^{2}-2*0.48*17

which is 3 m/s.

V

_{sf}=V

_{si}+at

3=5-0.48t

t=4.16s

They should finish the race at the same time, so this is also the time in which Mary ran 17 m.

X=V

_{o}t+1/2at

^{2}

22=4*4.16+a*(4.16)

^{2}

5=2.08*4.16*a

and a=0.60 m/s

^{2}

This is an internet assignment and the program says this result is false.

Is there a mistake here? What do I do wrong? Thanks for any help :)