Help finding kinetic and potentail.

[leonne]

Homework Statement

mass m1 rest on a frictionless horizontal table and is attached to a mass less string. The string runs horizontally to the edge of table passing threw mass less pulley and than mass2 hangs there.

Homework Equations

The Attempt at a Solution

I thought the kinetic would be
T=1/2 (m1$$\stackrel{.}{x}$$²) + m2$$\stackrel{.}{y}$$²)

and than potential would be U=gmy
but they have it as T=1/2 (m1+m2)$$\stackrel{.}{x}$$²)

U=-gmx

Why is this? I thought block 2 moves in the y direction so why is it given velocity in x direction same thing with potential and why is it negative?


thanks

 

[PhanthomJay]

Homework Statement

mass m1 rest on a frictionless horizontal table and is attached to a mass less string. The string runs horizontally to the edge of table passing threw mass less pulley and than mass2 hangs there.

What is the question?

I thought the kinetic would be
T=1/2 (m1$$\stackrel{.}{x}$$²) + m2$$\stackrel{.}{y}$$²)

This is the kinetic energy at a certain value of x and y, where x = y in magnitude, since they move together

and than potential would be U=gmy

yes, at a certain point y, but if the initaial value of y is taken as zero at the start point, then this term is negative, since y is negative

but they have it as T=1/2 (m1+m2)$$\stackrel{.}{x}$$²)

same answer as your's, where x = y, and the equation is then factored

U=-gmx

Yes ,see above, and note x = y

Why is this? I thought block 2 moves in the y direction so why is it given velocity in x direction same thing with potential and why is it negative?


thanks

Still confused? But what is the actual question?

 

[leonne]

the question is to write down the Lagrangian for the system and to solve for acceleration that part is easy just suck at figuring out the potential and kinetic lol