A boy standing on an overhead bridge overlooking a highway wanted to drop a stone on a truck passing under the bridge. He released the stone just as the front end of the truck passes directly below the railing. If the truck is traveling at 55km/hr and is 12m long, how far above the truck must the railing be if the stone just missed the rear of the truck?

Thanks.

Question

A boy standing on an overhead bridge overlooking a highway wanted to drop a stone on a truck passing under the bridge. He released the stone just as the front end of the truck passes directly below the railing. If the truck is traveling at 55km/hr and is 12m long, how far above the truck must the railing be if the stone just missed the rear of the truck? 

Thanks.

anonymous · Answer

First of all, convert 55km/hr to m/s.
You then find the time it takes the truck to travel 12m (<-the length of the truck).
Then you find the distance travelled by the rock which is also the height of the railing from the truck using the time using the equation: $$d=vt + \frac{ 1 }{ 2 }a t^{2}$$