Calculate the acceleration of each mass at the instant the thread snaps

[Josielle Abdilla]

Homework Statement

A piece of lead of mass 1.5 kg is suspended from a light spring. A copper sphere of mass 2.5 kg is suspended by keans of a thread as attatched to the lead. The thread is then burnt. Calculate the acceleration of each mass at the instant the thread snaps

Homework Equations

(Mv-mu/ t ) of the lead = mv-mu /t of the sphere

 

[kuruman]

What is that you are revising? Please show what you have done so far. Is the spring constant given?

 

[Josielle Abdilla]

I am revising the laws of motion and momentum. The spring constant is not given So far, I have only guessed that this situation is an explosion but nevertheless I can't think of how is it possible for the copper sphere to adopt an acceleration other than 10m/s. Do you have any ideas about this pls?

 

[PeroK]

No, I am revising the laws of motion and momentum. The spring constant is not given So far, I have only guessed that this situation is an explosion but nevertheless I can't think of how is it possible for the copper sphere to adopt an acceleration other than 10m/s

Just use $k$ for the spring constant and See what you get.

 

[FactChecker]

I assume that the initial condition is stable and nothing is moving. Then you can figure out how much force the spring is exerting at that position. That gives you its force at the instant that the string is cut. You should be able to calculate the answers from that.

 

[kuruman]

I am revising the laws of motion and momentum. The spring constant is not given So far, I have only guessed that this situation is an explosion but nevertheless I can't think of how is it possible for the copper sphere to adopt an acceleration other than 10m/s. Do you have any ideas about this pls?

You may treat it as an explosion that doesn't add kinetic energy to the two masses, so the treatment doesn't buy you much. Remeber that in a spring-mass system the acceleration is proportional to the displacement from the equilibrium position, the constant of proportionality being $\omega^2$. What are the equilibrium position and $\omega$ after the string is burned and the copper sphere drops?

 

[FactChecker]

Maybe I am missing something. I don't see any connection to an explosion. The dropping copper sphere is just being released to fall. The lead is just being pulled by a spring. IMHO, both are simple acceleration problems.

 

[vela]

I can't think of how is it possible for the copper sphere to adopt an acceleration other than 10m/s. Do you have any ideas about this pls?

Do you have a reason for thinking this answer is wrong?

 

[haruspex]

an acceleration other than 10m/s

It cannot be that since m/s does not express an acceleration.

 

[FactChecker]

The acceleration of the lead is slightly harder. The spring coefficient is not needed. How much force was holding the combined lead and brass before the string was cut? That force is still there after the string is cut.