# Homework Help: Some Questions

1. Feb 26, 2005

### lcg

I have these questions and I'm not sure which formula to use in each:

This one is confusing as the distances are in miles rather than kilometers:

1. A car is travelling north along a highway and the driver notices that, although the speedometer reads 60mph he actually covers a distance of 5 miles in 5.5 minutes. Calculate the speed of the car.

2. A child can produce a power of 200W. He has to shovel 1000kg of sand from his drive on to the back of a lorry which is at a height of 0.9m above the ground. What is the smallest energy required to shovel the sand?

3. Calculate the shortest possible time that he would need to shovel the sand on to the lorry.

Last edited by a moderator: Feb 26, 2005
2. Feb 26, 2005

### FredGarvin

1. What is the definition of speed? Isn't it change in distance per unit of time$$S = (\frac{\Delta X}{\Delta t})$$ ?

2. What is the definition of work? Isn't it a force applied over a distance $$W = F* \Delta X$$ ?

3. What is the deinition of power? Isn't it the amount of work per a unit of time $$P = (\frac{W}{\Delta t})$$ ?

For each of these equations, you have to make sure you are using the correct units for your values (e.g. in #1 you will have to convert 5.5 minutes into hours to end up with an answer in miles per hour).