# work power

a system consists of two cubes of masses m1 & m2 respectively connected by a spring of force constant k . find the force (F) that should be applied to the upper cube for which the lower one justs lift after the force removed

33
Abhishek Priyam ·

image is there or not [7] i am not able to see that..

62
Lokesh Verma ·

Sorry din read the question correctly :)

this question is solved on the forum already..... (it was by given by priyam.. )

let me find the question..

62
Lokesh Verma ·

priyam this is the same question as burning of thread... (only presented slighty differently)

33
Abhishek Priyam ·

This one:

http://targetiit.com/iit_jee_forum/posts/an_extension_309.html

33
Abhishek Priyam ·

here if F is applied in above direction then for lower block m2g=kx

for upper block F=m1g+kx

if the force is applied in downward direction then...... ;)

62
Lokesh Verma ·

yup this one only..

the only difference is that masses will change :)

1
big looser ......... ·

i have confusion in the equation F=m1g+kx

1
big looser ......... ·

plz help nishant

62
Lokesh Verma ·

aman the solution is a bit lengthy...

just give me a couple of hours i will try to post the full solution...

1
big looser ......... ·

ok brother , take your time

62
Lokesh Verma ·

sorry dudee a couple of hours have changed to a couple of days...

when u apply a force in the downward directin, the fbd of the upper mass will have its mg, F in the downward direction and kx in the upward

hence

F+mg=kx

1
Randheer Kumar ·

to lift both masses, force must be equal to total weight.

F=(m1+m2)g