Force Required to move heavy pendulum

[Curly23452345]

Hello,

In an attempt to end a very long and cringe-worthy debate I would like to ask this question.

How could one calculate how much force is required to move a 300lb pendulum(a heavy punch bag) to an angle of 90 degrees?

I have vague notions of how it could be done, but I certainly couldn't come up with a solid answer. I assume moments, angular velocity and impulse would come into it, but to be honest, I'm floundering.

Please, put a poor man out of his misery.

Thanks in advance,
Curly

 

[russ_watters]

Just calculate the force at 90 degrees. Hint: there is nothing to actually calculate.

...unless you are talking about a punch, in which case it isn't about force but impulse or energy.

 

[Curly23452345]

Just calculate the force at 90 degrees. Hint: there is nothing to actually calculate.

...unless you are talking about a punch, in which case it isn't about force but impulse or energy.

I see, how would one go about calculating the energy?

If a 135lb man were to throw himself at the pendulum, and pretending that the man transferred all his kinetic energy into the bag, how would it be calculated?

 

[sophiecentaur]

The question is a bit too open, I think. You could always just lift it - but I guess that's not what you want.
Gravitational Potential Energy is easy to calculate if you know how high it will be when at 90^o.
The kinetic energy after the 'punch' would have to be the same value, for it to get that high.
That will tell you the speed it needs to start its climb at and this will tell you the change in its momentum, which is the value of the impulse you need to give it (impulse is change in momentum and is force times the time the force acts).

 

[russ_watters]

Potential energy is mgh
Kinetic energy is 1/2mv^2

So if you want to start with all kinetic and end with all potential, you get mgh=1/2mv^2