### Video Transcript

Calculate the work done by a force of 13 newtons acting on a body that moved 40 meters to the north if the force was acting towards the south. State your answer in joules.

Remember, work is the measure of energy transfer when a force 𝐹 moves an object through distance 𝑑. We can use the formula work done is equal to force times distance to calculate it. Now, a little note about the units we work in. Work done is usually calculated in joules. This is only the case, though, if the force is measured in newtons and the distance is measured in meters. If the force is measured in dynes and the distance in centimeters, the work done is measured in ergs.

In this question, the force is in newtons and the distance is in meters, so our answer is indeed in joules. We’re going to need to be a little bit careful as well about the direction in which our force is acting and which the body is moving. The force is acting towards the south, whereas the body is moving towards the north. We could say then that the force is negative 13 newtons in the direction of the north. This means the work done is actually negative 13 multiplied by 40, which is negative 520 or negative 520 joules.

The work done by the force of 13 newtons acting on a body moving 40 meters to the north, given that the force is acting towards the south, is negative 520 joules.