- #1

AnnieD

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## Homework Statement

A 35kg box needs to be lifted to the top of a loading dock, which is also accessibly by ramp. The ramp is 5.0m long and has a vertical height of 1.7m.

a) What minimum force is required to lift the box straight up onto the loading dock?

b) What minimum amount of work is required to lift the crate straight up onto the loading dock?

c) What force is required to push the crate up the ramp such that the amount of work is the same as in b)? Assume no friction.

http://img178.imageshack.us/img178/3852/18qr9.png [Broken]

## Homework Equations

E = W

Ep = mgh

W = f x d

## The Attempt at a Solution

I solved all the problems:

First solved to get the angle of the ramp using sin law. It was 19.88, rounded to 20.

a) Ep = mgh

= (35)(9.8)(1.7)

= 583.1N

W = f x d

583.1 = F x 5(sin20)

F = 340.97N

b) solved in a (Ep) = 583.1N

c) W = F x d

583.1 = F x 5(cos20)

F = 124.1N

My question is in parts b) and c) where I used sin/cos. I knew those had to be used because it was at an angle, but only knew which to use because I compared my answers with those given in the answer section of the textbook. So how do I know when to use sin or cos, is one of the lengths of the diagram equal to work or force?

Thank you!

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