Car collision problem. Conservation of momentum

[physicgeek]

A 1100 kg car traveling initially with a speed of 25.0 m/s in an easterly direction crashes into the rear end of a 8200 kg truck moving in the same direction at 20.0 m/s . The velocity of the car right after the collision is 18.0 m/s to the east.

1.How much mechanical energy is lost in the collision?



Thank you

 

[rock.freak667]

Hello physicgeek, you need to post your attempt at the problem before anyone at PF can help you as per the rules.

 

[physicgeek]

Hello physicgeek, you need to post your attempt at the problem before anyone at PF can help you as per the rules.

sorry I am new.

what i did was i took the kinetic energy of both and subtracted them.
but i got it wrong on webassign. (online homework)

 

[rock.freak667]

sorry I am new.

what i did was i took the kinetic energy of both and subtracted them.
but i got it wrong on webassign. (online homework)

ah, I see. You forgot that that after the collision, the truck is still moving.

How would you go about finding the velocity of the truck? What law would you apply?

(Hint: it's in your thread title)

When you get that, find it for before the collision and after the collision and equate them.