- #1

gjh

- 10

- 6

- Homework Statement
- A motorcyclist driving in a 60-km/h zone hits a stopped car on a level road. The motorcyclist was thrown from his bike and landed 39 m down the road. Was he speeding?

- Relevant Equations
- vf(x)^2=vi(x)^2+2a(x)s -> 0 = vi(x)^2+2a(39) -> a (x)=-(16.7)^2/78=-3.57 m/s^2

60-kph = (60x1000)/60x60 = 16.7 m/s

vf(x)=vi(x)+at -> 0 = 16.7 m/s-3.57m/s(t) ->t=4.6 s

s=39=vt = v(4.6) -> v= 8.4 m/s

s=16.7(4.6)=76.8 m

I assumed the cyclist was going 60-kph. Then worked backwards as shown above to calculate the deceleration in the x direction and then the time to decelerate to a stop at 39 m. Then used this time to calculate the initial speed if cyclist thrown 39 m, which was 8.4 m/s. But if he was going 16.7 m/s, he would have been thrown 76.8 m. The answer is he was speeding, so I have the logic reversed or one of the equations is wrong. Grateful for any hints.