What Are the Energy Transformations in a Car-Truck Collision?

[lo31415926535]

Homework Statement

A 1110 kg car traveling initially with a speed of 25.0 m/s in an easterly direction crashes into the rear end of a 9900 kg truck moving in the same direction at 20.0 m/s (Fig. P9.21). The velocity of the car right after the collision is 18.0 m/s to the east.

image: http://www.webassign.net/sb5/p9-21.gif

(a) What is the velocity of the truck right after the collision?

(b) How much mechanical energy is lost in the collision? (Use input values with an adequate number of significant figures to calculate this answer.)

(c) Account for this loss in energy. (Select all that apply.)
Kinetic
Sound
Internal energy
Elastic Potential
Heat
Gravitational Potential

Homework Equations

m1v1i + m2v2i = m1v1f + m2v2f
K=.5mv^2

The Attempt at a Solution

So I figured out parts a and b, but I cannot get part c.
Honestly, I do not remember anything like this question from class.
So far I these were my guesses:
(1) just kinetic
(2) kinetic, internal, elastic
(3) kinetic, elastic

But the truth is I don't really know what this means, and I want to stop guessing and actually understand it…
I think kinetic would be one of them because both vehicles slow down.
I don't know what else though

Thanks for your help

 

[tiny-tim]

welcome to pf!

hi lo31415926535! welcome to pf!

(b) How much mechanical energy is lost in the collision? (Use input values with an adequate number of significant figures to calculate this answer.)

(c) Account for this loss in energy. (Select all that apply.)
Kinetic
Sound
Internal energy
Elastic Potential
Heat
Gravitational Potential

i think they mean account for mechanical-energy-before minus mechanical-energy-after

if all the energy was included (and not merely the mechanical energy), then the difference would be zero

so, essentially, they're asking you to list the energy that isn't mechanical energy

 

[HallsofIvy]

You should be able to drop "Gravitational Potential Energy" from that list- the vehicles don't go up at all! And the same for "Elastic Potential Energy". In fact just seeing "potential" in those should tell you they cannot be responsible for loss of mechanical energy in a collision.

 

[lo31415926535]

thank you both! i got it :)