# Trucks speed...

• Jan 30th 2009, 10:55 PM
lily123
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.
• Jan 31st 2009, 02:21 AM
earboth
Quote:

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 $v = 5u$

Plug in this term into the given equation:

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

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

Afterwards calculate v.

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