# Homework Help: Is This Right?

1. Jan 25, 2009

### Stratosphere

1. The problem statement, all variables and given/known data
You are trying to loosen a stuck bolt on your RV using a big
wrench that is 50 cm long. If you hang from the wrench, and your
mass is 55 kg, what is the maximum torque you can exert on the
bolt?

2. Relevant equations

T=Fr I did T=55kg*.5m

3. The attempt at a solution
I thought the answer would be 27 kg m^2
It doesn't seem quit right though.

2. Jan 25, 2009

### Elbobo

Force is not the same thing as mass. In this case, what kind of force results from your mass?

3. Jan 25, 2009

### Stratosphere

So you mean i have to turn the weight into GE or KE?How could it be GE if i dont know the height?

4. Jan 25, 2009

### Elbobo

No, weight IS the force you want. But mass is not the same as weight.

5. Jan 25, 2009

### Stratosphere

But if it says 55kg or mass doesnt it mean weight?

6. Jan 25, 2009

### NBAJam100

no, mass is not the same as weight.use w=mg of F=ma

7. Jan 25, 2009

### Elbobo

Weight is the force of gravity. The force of gravity equals mass * acceleration.

Mass is NOTTTTTTTTT the same as weight.

8. Jan 25, 2009

### Stratosphere

How do i know the velocity?

9. Jan 25, 2009

### Elbobo

Let me reiterate with more definition:

Weight = mass * acceleration due to gravity (this will be, in most problems, a constant)

Acceleration due to gravity is otherwise known as g = 9.8 m/s^2.

10. Jan 25, 2009

### psykatic

Well, the acceleration is basically the pull of the earth, called acceleration due to gravity. It has a fixed value of 9.8 or approximately 10!

11. Jan 25, 2009

### Stratosphere

so the answer is 269.5? and using w=ma i got that the guy is 539 kilograms.

12. Jan 25, 2009

### Elbobo

Oy.... Weight, when calculated by kg and m/s^2, is in newtons (N).

It would be 539 N, not kg. How can you multiply kg * m/s^2 and get kg?

And yes, that's the correct number in Newtons.

13. Jan 25, 2009

### Stratosphere

So the right answer is 269.5? What units would it be in?

14. Jan 25, 2009

### Elbobo

Oh, sorry. Torque is force times the radius. You multiply the units of force and the units of the radius together to get the units of torque.

Figure it out.

15. Jan 25, 2009

### NBAJam100

Look at the equation to find units. Your equation is the most valuable thing you have to determine units.

torque=F*r correct? So units of Force are Newtons and units of radius are meters...

So wouldnt it make sense to having units of torque be N*m?

16. Jan 25, 2009

### Stratosphere

Now I got 134. I did 539*.25m.

17. Jan 25, 2009

### Elbobo

You meant to put 0.5 m, not 0.25m.

What are the units of velocity?

We know velocity equals distance divided by time.

v = d/t
Distance is usually in meters, and time is usually in seconds.
units of v = units of distance / units of time
units of v = meters / seconds
units of v = m/s

Do the same for torque.

18. Jan 25, 2009

### Stratosphere

so can any at least tell if its wrong?

19. Jan 25, 2009

### Elbobo

20. Jan 25, 2009

### LowlyPion

Let me recommend that the OP read :
http://en.wikipedia.org/wiki/Weight#Weight_and_mass

Torque is based on the distance the Force acts.

Hence m*g*Lhandle = Torque in units of N-m

As for the answer 134 it looks like the Length of the handle is not used correctly.