# How to work out this impact force

1. Sep 5, 2016

### Lily May

1. The problem statement, all variables and given/known data
During a Formula 1 race a car that was travelling at a speed of 172.8 km/h crashed into a wall. When the car hit the wall it came to a complete stop in 0.0272 s. If the driver of the car holds a mass of 70kg, calculate the impact force he experienced.

2. Relevant equations
I honestly don't know. F = m*a or F= GMm/r^2

3. The attempt at a solution
I have no idea what to do???
F= m*a
= 70*172.8
= 12 096N

2. Sep 5, 2016

### Staff: Mentor

I don't think gravity will have anything to do with this problem, so you can forget that last equation.

What is the acceleration (meaning "deceleration" in this case) of the car as it hits the wall?

3. Sep 5, 2016

### Staff: Mentor

Does the unit for acceleration match the unit of the number you've plugged in for 'a'? If not, how might you get that unit from the information provided?

4. Sep 5, 2016

### Lily May

Am I meant to use the acceleration formula for that?
a= v1 - v2 / t

5. Sep 5, 2016

### Staff: Mentor

Yes. [But it should be v2 - v1 if v2 is the final velocity. And parentheses can be helpful: a = (v2 - v1)/t.]

6. Sep 5, 2016

### Lily May

So you'd have to mutiple the number by 1000 then divide by 3600?
172.8*1000= 172800
172800/3600= 48m/s/s

7. Sep 5, 2016

### Staff: Mentor

Put units everywhere:
\begin{align*} 172.8\frac{\mathrm{km}}{\mathrm{h}} \times \frac{1000\ \mathrm{m}}{\mathrm{km}} &= 172800 \frac{\mathrm{m}}{\mathrm{h}} \\ 172800 \frac{\mathrm{m}}{\mathrm{h}} \times \frac{\mathrm{h}}{3600\ \mathrm{s}} &= 48 \frac{\mathrm{m}}{\mathrm{s}} \end{align*}

8. Sep 5, 2016

So
v2 = 0?
v1= 48m/s^2
t = 0.0272s

9. Sep 5, 2016

### Staff: Mentor

DC seems to be helping you well at the moment. I'm going to step out and let him handle it for now. I'll pop back in later though.

10. Sep 5, 2016

### Lily May

Whoops, I'll be sure to do that, thanks. So then do I use the acceleration fomula or the force fomula?

11. Sep 5, 2016

### Staff: Mentor

Are you sure about the units of v1? What is the acceleration?

12. Sep 5, 2016

### Lily May

v1 = 48m/s
a = (v2 - v1)/t.]
= 0 - 48m/s
= -48m/s / 0.0272s
a = -1 764.71m/s
that doesn't seem right

13. Sep 5, 2016

### jbriggs444

Units... if you divide meters per second by seconds, what do you get?

14. Sep 5, 2016

### Staff: Mentor

The math looks correct, you just have it in units of velocity instead of acceleration.

15. Sep 6, 2016

### Lily May

So I'd just change the end to -1 764.71m/s^2 = a
And mass = 70kg
Then I multiple those two together to get the impact force/final answer?

16. Sep 6, 2016

### Staff: Mentor

Correct.

17. Sep 6, 2016

### Lily May

Thank you all!

18. Sep 6, 2016

### BvU

Bit of a macabre exercise. 180 g can not be survived by a human. This looks like a post mortem review ..
Fortunately head-on crashes with concrete walls are rare in F1.