What happened to the kinetic energy?

[pivoxa15]

Homework Statement

A fork-lift truck lifts a crate of machinery parts of mass 600kg from the floor of a warehouse and transports it at a steady speed of 1.5m/s on to the back of a semi-trailer that is 1.5m above the ground.

What happens to the kinetic energy of the crate when the fork-lift stops?

Homework Equations

none

The Attempt at a Solution

Energy must be conserved. I like to say that the kinetic energy it gained was supplied by the truck which it obtained from the burning of fuel. When the fuel stops burning, energy in the system is reduced and one type of energy that will vanish when the fuel stops burning is kinetic energy of the fork-lift. So to answer the question, when the fork-lift stops, the kinetic energy of the crate has gone because fuel energy is gone. But does that doesn't sound too right does it? Although I can't see anything wrong with it.

 

[Hootenanny]

Think about friction and the brakes of the fork lift.

 

[pivoxa15]

I was thinking too idealistically, the forklift doesn't suddenly stop when the engines are turned off. If no braking is applied than it stops due to loss of friction energy in the hinges etc. However, realistically it stops suddently and that will be because of braking so friction in the disk pads. So the kinetic energy is converted into heat energy either way.

 

[Hootenanny]

I was thinking too idealistically, the forklift doesn't suddenly stop when the engines are turned off. If no braking is applied than it stops due to loss of friction energy in the hinges etc. However, realistically it stops suddently and that will be because of braking so friction in the disk pads. So the kinetic energy is converted into heat energy either way.

Sounds good to me