Solve the below given problem:
 
A truck moving at \(20\ m/s\) has a kinetic energy of \(90000\ J\).

1. Determine the mass of the truck.
2. If the speed is reduced to \(7\ m/s\), calculate the new kinetic energy.
3. Calculate the work done by the brakes.
 
1. The mass of the truck \(=\) \(kg
2. The new kinetic energy \(=\) \(J\)
3. The work done by the brakes \(=\) \(J\)
 
[Note: Enter the answer upto two decimal values]