A car weighing 1200 kg is uniformly accelerated from rest and covers a distace of 40m in 5 sec. calculate the work done by car engine

The work done on a body is always the change in its kinetic energy (final - initial).

Now, as the car was at rest then the initial kinetic energy is zero, so the work done will be

W = KE = (1/2)mv²

here m = 1200 kg

and v = distance/time

  = 40/5 = 8 m/s

so, the 

W = (1/2) X 1200 X (8)² = 38400 J