Help with Kinetic Energy concept of two masses that move the same distance

[riseofphoenix]

Help with Kinetic Energy concept of two masses that move the same distance!

I don't understand why the answer to this is B :(

Because KE = (1/2)mv², if they move the same distance and have DIFFERENT masses, the kinetic energies would be different no?

 

[ekkilop]

Don't forget that the KE depends on the speed of the blocks, not just the masses and certainly not (at least not explicitly) the distance they move.
Hint: consider instead the amount of work done by the force on the masses.

 

[riseofphoenix]

Oh ok I think I understand...

 

[haruspex]

Because KE = (1/2)mv², if they move the same distance and have DIFFERENT masses, the kinetic energies would be different no?

It's natural to assume that the force is applied for the same duration to each, but you are not told that. In fact, it cannot be so. Hence, the speeds can be different although the distances are the same.

 

[Nickie]

Yes, you are correct. If two masses move the same distance, their kinetic energies would be different if they have different masses. This is because kinetic energy is directly proportional to mass - the greater the mass, the greater the kinetic energy. Therefore, if two masses move the same distance, the one with a greater mass would have a greater kinetic energy. However, if the two masses are equal, then their kinetic energies would also be equal.