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So for this question there is a man running through a section of grass 1.14375m long at a speed of 3m/s. How do i find his time do i assume the initial velocity is 0? Because that is the only way it works.

If i do that i use to find acceleration v^2 = u^2 + 2as 9 = 0 + 2*1.14375a a = 3.934

from that i use to find the time v = u + at 3 = 0 + 3.934t t = 0.76s

time is 0.76s

user151764
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  • I suppose that $3$ m/s is the average velocity of the man over his running time. Since you don't have any other information, I should use $d = v t$. Moreover, the time is so short that you can assume that for runnin a so short distance, the velocity is constant. – Claude Leibovici May 29 '14 at 09:46

1 Answers1

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I think it's much simpler : $$\delta t = \frac{\delta x}{v}$$ where $\delta x = 1.14375m$ and $v=3m/s$

But if you want to do the calculus with the acceleration, it's possible too :
The guy has his weight and the reaction of the floor, which means that the acceleration is equal to $0$. So the speed is constant and equal to $3m/s$ (I think the question assumed that the guy starts with a speed of $3m/s$)

Fabien
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