Calculating Tension: Pulley System with Different Masses | PhysicsForums

[botab]

Hello PhysicsForums

I need help with a certain question which has been bugging me for a while.

a pulley is suspended by a cord with two masses attached. one mass is 1.2 kg. the second mass is 3.2 kg. the two masses are attached on different sides.

the question: determine the tension in this cord after the masses are released and before one hits the ground. ignore the mass of the pulley and cords.

Thanks

 

[LowlyPion]

Welcome to PF.

Draw a force diagram for each of the weights.

The heavier one will be showing a Tension and a net force from the weight greater than the tension. The opposite will be true for the lighter one.

From your 2 equations Tension must be the same. Solve for acceleration and plug back into one of the equations.

 

[botab]

Thank you for replying, but the thing is for this question i don't think the acceleration is needed.. because were trying to find C is attached to the wall and the pulley. Then I thought of Fnet = t-mg and since Fnet = ma which has no acceleration. So I figure it would be 4.4*9.8 but I was wrong.. here is a picture of what I'm talking about.

Thanks again

 

[LowlyPion]

But there is a net force. 3.2 - 1.2 masses create a net force.

The system is accelerating.

If it was constant speed, the tension on one side would equal the weight and the tension on the other would equal that weight.

 

[botab]

ok thanks again ... I figured for 17.12N for tension ... and what I am now suppose to do now? Do I make basically sum up what I know that Fnet = mg-t? where mg is (3.2+1.2)(9.8) and Fnet is is (3.2+1.2)(4.45)?

 

[LowlyPion]

I thought tension was what you were solving for?

 

[botab]

we are solving tension, but its not the tension of the string with the weights on it. we are solving the tension of the pulley carrying the string& weight. I believe i sent an image on post#3. Does this change how the concept of how we are solving it?