What is the Force Exerted by a Pebble on a Block in an Ideal Atwood's Machine?

[taskev21]

Homework Statement

A pebble of mass m rests on the block of mass of m2 the ideal Atwood's machine in the figure below. Find the force exerted by the pebble on the block of mass m2. (Use the following variables as necessary: m for m, m_1 for m1, m_2 for m2, and g for gravity.)

Homework Equations

The Attempt at a Solution

i dont' know where to begin- -help!

 

[thebigstar25]

since you are just dealing with the pebble and the block which it rests on it .. it should be obvious that the pebble can only exert one force on that block since it has a certain mass m .. can you guess what should it be?