Question

A truck is travelling at 30km/hr with engine delivering a driving force of 800n to the road

Answer 1

Power = (force) x (distance / time) = force x speed .

We know the force = 800N.
We have a speed = 30km/hr, but in order to use it in the power formula,
it has to be in meters/second, so we have some work to do first.

(30 km/hr) x (1,000 m/km) x (1 hr / 3,600 sec) = 300 / 36  m/sec .

Power = (force) x (speed) = (800 N) x (300/36 m/s) = 6-2/3 kilowatts

Work = (power) x (time) = (6,666-2/3 joule/sec) x (25sec) = 166,666-2/3 joules.

The figure for power is slightly weird ... 746 watts = 1 horsepower,
so the truck's engine is only delivering about 8.9 horsepower.
Very fuel-efficient, but I don't think they drive trucks that way.