Perfectly Inelastic and initial kinetic energy

[jan2905]

An object of mass m (O1) moving with speed v collides head-on with a target object of mass 2m (O2) initially at rest. If the collision is perfectly inelastic, what fraction of O1's initial kinetic energy is lost?



1/2(m1)v^2initial=1/2(m1+m2)v^2final

m1v1=(m+2m)v2

v2=1/3(v1)

so...

1/2(m1)v^2=1/2(m1+m2)(1/3*v)^2 ... is this right so far?

 

[chrisk]

Take the ratio of the final kinetic energy to the initial kinetic energy. These two are not equal to each other unless you include a ratio factor on the left side of the equation.

 

[jan2905]

1/3? 3m*(1/9)v^2 yields a factor of 1/3.

 

[chrisk]

Correct.