# Homework Help: Kinetic energy of bow and arrow

1. Nov 27, 2008

### iFat

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

2. Relevant equations

3. The attempt at a solution

The question is if a meter stick is drawn in a bow so that it has 40 J of potential energy. When fired horizontally, the meter stick will have kinetic energy of _____.

A) Less than 40 J B) More than 40 J C) 40 J

I think it's C because of the conversation law. Energy can't be created or destroyed, but transformed. The energy is changing from potential energy to kinetic energy, but then I say it might be A.

The Winterchester Potato Cannon applies a 6000N average force to a 0.5 kg potato while the potato is in the 1.5 meter barrel. Assuming no friction, what is the change in KE of the potato?

A) 9000 J B) 6000 J C) 0J D)4500 J E) 4000J

For this question, I'm extremely confused. I don't even know what it's asking.

A pendulum is lifted so that it is raised 5 meter above its lowest position. When released, what is its maximum speed?

A) 5 m/s B) 7.07 m/s C) 10 m/3 D) 100 m/s E) need to know the mass

For this question, I think you have to know the mass because the formula is KE = 1/2mv^2. How can you figure out the maximum speed without the mass.

Last question, which of the following are not units of Power?

A) Nm/s B) J/s C) kgm2/s3 D) W E) Jm/s

I think it's C and E. I just wanted to double check just to make sure that answer was correct.

2. Nov 27, 2008

### arunbg

1. C seems correct if P.E is attributed to the drawing of the bow alone.

2. Hint: Work Done = Force * Distance

3. mgh = 1/2mv^2, do the masses matter now?

4. Check again

Oh and welcome to PF :)

3. Nov 27, 2008

### iFat

Thank you, that helped.

For 1) I got C.

2) A

C) C

and still working on 4. =)

4. Nov 27, 2008

### iFat

and the last one is E. =]

5. Nov 27, 2008

### arunbg

Looks good to me :)