# Physics problem

• Apr 16th 2013, 09:32 AM
Paze
Physics problem
Car A is still and starts driving as soon as car B drives past it with the speed 18m/s. Car A has acceleration 2,2m/s^2.

How long does it take for car A to catch up with car B?

This one is hitting me from the left field. I'm not close to solving it at all. Any help is appreciated. Please bear in mind that I am very new to physics when presenting a solution/directions. Thanks.
• Apr 16th 2013, 10:52 AM
Shakarri
Re: Physics problem
let t=0 be the time B passes A.
after a time t, B has traveled 18t meters and A has traveled 0.5(2.2)t2 (From the formula s= ut + 0.5at2)
• Apr 16th 2013, 11:18 AM
HallsofIvy
Re: Physics problem
Another way to do this: set up everything "relative to B". Initially, the distance between A and B is 0 but A's speed, relative to B, is -18 m/s. At time t, A's distance from B is \$\displaystyle -18+ 1.1t^2\$.
• Apr 16th 2013, 02:21 PM
Paze
Re: Physics problem
Thanks guys. Is 16,4 sec. the correct answer then? :)