# 2-body problems-Need help calculating!

2-body problems--Need help calculating!

A 20 kg block (A) rests on a frictionless table; a cord attached to the block extends horizontally to a pulley at the edge of the table. A 10 kg mass (B) hangs at the end of the cord.
a) Clearly draw and label the force vectors acting on each object.
b) Calculate the acceleration of the block and mass.
c) Calculate the tension in the cord.

I do not understand how to calculate the Net force. I do know that I need the Net force to get the acceleration of the block and mass, because FNet= m * a.
Also, I need help on calculating the tension in the cord as well. I don't know which numbers to use or how to get numbers for the equation if they aren't a given...
Thanks so much!
-Genevieve

## Answers and Replies

Your starting point is to realise that the tension, T, in the connecting cord exerts a horizontal force,T, on the 20kg block and a vertical (up) force of T on the 10kg mass.
Draw this diagram and apply F=ma to each object. (simultaneous equations !!!)

Or.... you could realise that there is only 1 external force........ due to the WEIGHT of the hanging 10kg block, and this force accelerates all of the mass of the blocks. This will give you the acceleration straight away but you will then need to calculate the tension in the connecting string.

ehild
Homework Helper

Genevieve, the first thing to do is to draw a picture, and "Clearly draw and label the force vectors acting on each object."

Show that drawing, please.

ehild