Inelastic collision, determine ratio KEf/KEi

[Anonymous123451234]

Consider the following extreme cases for a completely inelastic collision. In each case, determine the approximate ratio KEf/KEi.
a) A moving train collides with a stationary car.
b) A moving car collides with a stationary train.

I do not understand this question, I'm not given masses or velocities. Can anyone explain?

 

[mfb]

You can use typical values, the answer won't depend on your specific choice. You are asked for approximations. A car might have a mass of 500 kg (very light car) or 3000 kg (very heavy car), but it won't have a mass of 10 kg or 100,000 kg.

 

[DoItForYourself]

Hello,

I suppose KEf/KEi is the ratio Final Kinetic Energy / Initial Kinetic Energy.

You must answer the following questions:

1) What will be the final velocity (approximately) in each case?
2) What will be the final mass of the two bodies in case (a)?
3) What is the ratio Final Kinetic Energy / Initial Kinetic Energy (simplify the fraction till you get a number)?
4) What is the acceptable range for KEf/KEi value?

 

[haruspex]

Consider the following extreme cases for a completely inelastic collision. In each case, determine the approximate ratio KEf/KEi.
a) A moving train collides with a stationary car.
b) A moving car collides with a stationary train.

I do not understand this question, I'm not given masses or velocities. Can anyone explain?

Rather than plug in numbers (pace @mfb), I would create unknowns: m for the mass of the car, M for the much larger mass of the train, and u for collision speed. Once you have the formulae for the energy ratios, you can consider how they are affected by the mass ratio.