1. A train car with mass 2 M moving at 10.0 m/s collides with an initially stati

Question

1. A train car with mass 2 M moving at 10.0 m/s collides with an initially stationary train car with mass 3 M. The train cars couple together. What is the velocit of the two train crs after the collison? and what is the ratio of the final to the initial kinetic energy, kEf/ KEi?

2. what is the kinetic energy of a 67 g object moving at 45 cm/s? Give your answer both in the units given, as well as in standard sl units. That combination of the original units is called an erg, while the combination of sl units is called a Joule.

3.ke= 1/2 mv^2 and ke= p^2/ 2m

starting from the second expression and the definition of momentum p= mv, show that you can end up with the first expression.

Explanation / Answer

1) V2 = (m1/(m1+m2))*V1 = (2M/(2M +3M))*5 = (2/5)*5 = 2 m/s

kEf/ KEi = m1/(m1+m2) = 2M/(2M +3M) = 2/5

2) KE = (1/2)mv2 = (1/2)*0.067*(0.45)2 = 6.78*10-3 J

3) Ke = P^2/2m

Now P = mv

So Ke = (mv)^2/2m = (1/2)mv^2

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