Question

A truck driver can load oil drums into the back of the truck by pushing them up a sloping plank, or by lifting them directly. Each drum has a mass of 80 Kg, and the plank is 3 m long. Assume the back of the truck is 0.8 m lifted above the ground.

(i)  How much force would be needed to lift a drum into the truck directly, without using the plank? (Take g = 10 m/s²)?

(ii)  How much energy would be converted in lifting the drum into the truck without the plank?

(iii)  If the force needed to push a drum up the plank is 300 N, why is this less than the answer to question (i) ? 

(iv)  When the truck is loaded, the driver drives off. List the major energy changes that take place in moving the truck.

(v)  The driver has to stop at the factory gates. What happens to the kinetic energy of the truck?

Answer 1

(i)  Mass of the drum = 80 kg.

and g = 10 m/s²

Force of gravity on drum = m g = 80 x 10 = 800 N.

(ii)  Force of gravity on drum = 800 N.

Total distance covered = 0.8 m

Work done by the driver = Force x Distance = 800 x 0.8 m = 640 J.

Energy converted = m g h  = 640 J.

(iii)  When the force needed to push a drum up the plank is 300 N which is less than the answer to part

(i)  because plank make an angle with the road thus making an inclined plane which decreases the force or the efforts acting on the drum to push it up into the truck.

(iv)  The force exerted by the engine of the truck moves the truck and this work done by the force changes into K.E. of the truck

(v)  When the driver has to stop at the factory gate this K.E. is converted into the work done by the resisting force to stop the truck.