What's the least force we should apply?

[PhysicS FAN]

Homework Statement

2 objects of the same mass are on a non-frictional level and are connected with a thread which has a resistibility limit T=20N. What is the least froce we should apply so that the thread breaks?

Homework Equations

The Attempt at a Solution

I don't know how to proceed with this problem since the system contains of 2 objects. My first thought was to use kinetic energy theorem on the first body since Kτελ-Καρχ=0 and then find a relationship with the tension of the thread and the force based on the energy theorems but that didnt work. Please help me

 

[PeroK]

You need to think about all the forces on your system.

 

[PhysicS FAN]

You need to think about all the forces on your system.

Yes there's the force that we apply and the tension.

 

[PeroK]

Yes there's the force that we apply and the tension.

What happens when you apply a force?

 

[PhysicS FAN]

What happens when you apply a force?

Well in this case the force will accelerate the system which may or may not had an initial velocity. If the force is big enough it will break the thread. Now after the thread breaks the left object will continue moving with the speed it had just before the moment that the break of the yarn happened because there is no friction and accroding to Newtons 1st Law it will continue moving. In the left object the force that is causing the acceleration is the tension of the thread so T=m*a . In the second object the tension is in the opossite direction of the force so: F-T=m*a. Now if we solve for F we get F=m*a+T . But from the first equation we know that m*a= T and so the force is equal to F=2T=2*20=40N.
I don't know what you did but you helped me solve the problem with only a question. Thank you!