(adsbygoogle = window.adsbygoogle || []).push({}); A 2000kg car travelling to the right at 30 m/s is chasing a second car of the same mass that is travelling to the right at 10 m/s

1) if the two cars collide and stick together, what is their speed after the collision?

2) What fraction of the initial kinetic energy of the cars is lost during this collision?

Ok so i'm pretty sure i've got the first question answered using the formula for calculating momentum (Momentum = Mass * Velocity) but i'm having a bit of trouble answering question 2. The collision should result in a loss of kinetic energy but i've come up with an answer that says it has gained kinetic energy :S.

Here is the work I have done thus far:

1) Momentum Before = (2000kg * 30m/s) + (2000kg * 10m/s)

= 80, 000 kg m/s

therefore V after = (Momentum1 + Momentum2)/(Mass1 + Mass2)

= 80,000kg m/s / 4000kg

= 20m/s

2) KE1 = 1/2 MV^2

= 1/2 2000 * 30^2

= 900,000 J

KE2 = 1/2 MV^2

= 1/2 2000 * 10^2

= 100,000 J

Therefore total initial KE = 1,000,000 J

Therefore KE after = 1/2 (m1 + m2) * (total velocity)

= 1/2 8000 * 20

= 1,600,000 J

Any help would be greatly appreciated!

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# Homework Help: Two cars colliding

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