Tension in a String: Explaining P=T+25 N vs P+T=125

[Lori]

Homework Statement

Homework Equations

Ook, so I'm really bad at physics, and i need someone to help explain why the answer is P=T+25 N
I thought it is P+T = 125

The Attempt at a Solution

Since the system is in constant velocity, then Fnet = 0 so that P + T + W = 0 Why isn't it P + T + 125 =0?[/B]

 

[jbriggs444]

Which direction does T pull on the 100 N weight?
Which direction does T pull on the 25 N weight?

 

[Lori]

Which direction does T pull on the 100 N weight?
Which direction does T pull on the 25 N weight?

T always pull away from the object. So, for the 100 N weight, Tension pulls downward and for 25N, the tension pulls upward

 

[haruspex]

T always pull away from the object.

Yes.

So, for the 100 N weight, Tension pulls downward ...

Away from the 100N weight would be upwards, surely?

 

[CWatters]

Perhaps draw a two free body diagrams, one for each mass.

 

[Lori]

Perhaps draw a two free body diagrams, one for each mass.

Thanks , i drew it for the 25 N object and got that P = T+25!

 

[Lori]

I have a question to add!
If i know that W = T for the second diagram , then I know that T = 100N right?

I can actually find P since P = 25+T , so that P=125

 

[jbriggs444]

If i know that W = T for the second diagram , then I know that T = 100N right?

I can actually find P since P = 25+T , so that P=125

Right!