Tension of a string passing over a pulley

[zcabral]

Homework Statement

A 2.50 kg object placed on a frictionless, horizontal table is connected to a string that passes over a pulley and then is fastened to a hanging 7.50 kg object, as in Figure P5.24. Find the magnitude of the acceleration of the two objects and the tension in the string.

Figure P5.24:http://www.webassign.net/pse/p5-24alt.gif

acceleration of 2.50 kg object

acceleration of 7.50 kg object

tension in string

Formulas:

F=ma
T=ma

Work:

well i figured out the second part that the acceleration is 7.35. i used the formula a=F/m. F= 9.8 X 7.5. however i tried to doing the same for the first 1 and it said the answer was wrong. i did a=F/m. F=2.5x9.8=24.5/2.5=9.8 which was wrong. also for the tension i can't figure it out until i find the a for first part. then i plan to use the formula...T=2m1m2/m+m2*9.8...would that be the right forumla?

 

[Doc Al]

Since they are connected by a string, both masses have the same acceleration (in magnitude). Instead of plugging into a formula, apply basic principles. Analyze the forces on each mass and make use of Newton's 2nd law. You'll get two equations, which you can then solve to find the two unknowns: acceleration and tension.