You lift a 450 newton bag of rice 1.2 metres and carry it a distance of 10 metres to the kitchen. How much work is done?

Hello!

The physical work, by the definition, is the product of the force, the displacement AND the cosine of the angle between them. Recall that both force and displacement are vector quantities. In other words, we can say that the work is the dot product of the force and the displacement.

The definition above is applicable only for a movement with a constant force and a constant angle between a force and a displacement. For several such movements the works are added.

In our problem there are two such movements: up and forward. During the first part the displacement is directed upwards, during the second -- horizontally. The force is the reaction one, it is the same in magnitude as the weight and is directed upwards.

So at the second part no work is done because the angle is 90° and its cosine is zero. At the first part the angle is 0 and its cosine is 1, so the work is

450N*1.2m*1=540J. This is the answer.