# How to calculate Speed?

1. Jul 10, 2013

### wangwang2626

How do you calculate the speed at which one objects hits another. I know the initial speed , the deceleration and the distance. Is there anything else I need to know.
The car was travelling at 110km/h it decelerates at 6.5 m/s and hits a wall 25m away . so what formula do I use to calculate the speed at which the car hits the wall? Could I in any way also calculate the amount of time it took until the car hit the wall?

2. Jul 10, 2013

### Curious3141

Are you familiar with $v^2 = u^2 + 2as$ for the first part?

In kinematic problems, it's often helpful to list all the relevant equations, then write down which quantities you know, and which you need to determine in two columns. Then pick the best equation(s) for your purpose.

After you follow my advice, you should be able to select the correct equation to do the second part as well.

3. Jul 10, 2013

### Mandelbroth

$2a\Delta{x} \approx v^2-v_0^2$
$\Delta{x} \approx v_0t+\frac{a}{2}t^2$

4. Jul 10, 2013

### wangwang2626

Thank you

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