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

[Senjai]

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

Homework Statement

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.

Homework Equations

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

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

 

[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 $F_{applied}$

 

[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.

 

[RoyalCat]

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.

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. :)

 

[Senjai]

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

 

[G01]

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

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

 

[Senjai]

Thanks for all your help guys!