# W=Fd, Work & Newton's Second Law problem

1. Oct 10, 2009

### Senjai

[SOLVED] W=Fd, Work & Newton's Second Law problem

1. The problem statement, all variables and given/known data

a) Find the force to give a helicopter of mass M an acceleration of 0.10g upward
b) Find the work done by this force as the helicopter moves a distance of h upward.

2. Relevant equations

$$W=F_{net}d$$
$$F=ma$$

3. The attempt at a solution

Personal Note: Q10 p. 145 Challenger.

This question isn't in the answer key, this post is mostly to verify my answer and figure it out if it's wrong.

I first stated F = Ma, then stated a = 0.10 x 9.8 m/s^2 = 0.98 m/2^2

Then for my answer, i had $$F=M(0.98_{m/s^2})$$

would that be the proper way to state that answer?

b)
I stated W = Fd
Then stated W = M(0.98m/s^2)h

is this correct?

Thanks,
Senjai

Last edited: Oct 10, 2009
2. Oct 10, 2009

### G01

For part a), the net force=0.1g

Remember:

$$0.1g=F_{net}=\sum F$$

You should be able to find the correct, applied force on the helicopter.

Part b) is done correctly, except you need to use the correct $F_{applied}$

3. Oct 10, 2009

### Senjai

Oh, this isn't the first time questions worded with g and a coefficient has stumped me.

g = 9.8 m/s^2 right?

oh.. so your saying an acceleration of 0.1g so F = 0.1(9.8)?

I have trouble understanding exactly how it's asking for what... it's asking.

4. Oct 10, 2009

### RoyalCat

You aren't asked about the net force. You are asked what force it would take to raise the helicopter with a constant acceleration of $$0.1 g$$

What forces act on the helicopter? There's $$F_{applied}$$ as GO1 mentioned, but there is another force acting on the helicopter as well.

Find out what force that is, plug everything into Newton's Second Law and isolate for $$F_{applied}$$ from there on out, you're good to go. :)

5. Oct 10, 2009

### Senjai

So: Fapplied = M(0.1g) + mg?

6. Oct 10, 2009

### G01

Correct!, except the "m" in the second term, should be "M" in the notation of the problem. There is only one mass, M.

7. Oct 10, 2009

### Senjai

Thanks for all your help guys!