Calculating Maximum Torque to Loosen Stuck RV Bolt

[Stratosphere]

Homework Statement

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?

Homework Equations

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

The Attempt at a Solution

I thought the answer would be 27 kg m^2
It doesn't seem quit right though.

 

[Elbobo]

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

 

[Stratosphere]

So you mean i have to turn the weight into GE or KE?How could it be GE if i don't know the height?

 

[Elbobo]

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

 

[Stratosphere]

But if it says 55kg or mass doesn't it mean weight?

 

[NBAJam100]

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

 

[Elbobo]

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

Mass is NOTTTTTTTTT the same as weight.

 

[Stratosphere]

How do i know the velocity?

 

[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.

 

[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!

 

[Stratosphere]

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

 

[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?

Read your textbook or your notes more.

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

 

[Stratosphere]

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

 

[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.

 

[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 wouldn't it make sense to having units of torque be N*m?

 

[Stratosphere]

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

 

[Elbobo]

You meant to put 0.5 m, not 0.25m.

Example of finding your units:

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.

 

[Stratosphere]

so can any at least tell if its wrong?

 

[Elbobo]

Read my entire posts...

 

[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*L_handle = Torque in units of N-m

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

 

[Stratosphere]

So now i got 269 if i don't use the radius of the handle.

 

[Stratosphere]

so if no one answers i guess i have it right then. Right?

 

[LowlyPion]

So now i got 269 if i don't use the radius of the handle.

Looks OK. Units are N-m right?

The radius of the handle?

Think Length not radius. The wrench is a moment arm of length .5m