# Thread: Trucks speed...

1. ## Trucks speed...

A truck is accelerating over a certain distance (in metres). Its final speed (v m/s) is related to its starting speed (u m/s), according to the rule v²=u²+1500. Find the truck's starting and final speeds, given that the truck's final speed is 5 times its starting speed.

2. Originally Posted by lily123
A truck is accelerating over a certain distance (in metres). Its final speed (v m/s) is related to its starting speed (u m/s), according to the rule v²=u²+1500. Find the truck's starting and final speeds, given that the truck's final speed is 5 times its starting speed.
Let u denote the starting speed. Then you know that $\displaystyle v = 5u$

Plug in this term into the given equation:

$\displaystyle (5u)^2=u^2+1500$

Solve for u. (The negative solution isn't very plausible here)

Afterwards calculate v.

I've got $\displaystyle v\approx 39.53\ \frac ms$. That means the final speed of the truck is $\displaystyle 142.3\ \frac{km}h$. In Germany the truck driver would be arrested by the police immediately