Physics again, masses/pulleys, accel, tension

[MikeMike]

Originally posted by: Hacp
stupid junior! Listen in class!

huh? im a sophmore in college.

 

[kevinthenerd]

Originally posted by: nourdmrolNMT1
well i would divide 10N by 1kg. but im confused, i used to know how to do this, but forgot. i took AP phys two years ago, now im in College Physics and forget how to do the basics.

Oh, that sucks! I took AP physics, and then I tried to take Physics II two years later (because I only got a 3 on Electricity and Magnetism). It just about killed me. I knew just enough to be dangerous, and it was hard filling in the gaps.

 

[MikeMike]

Originally posted by: kevinthenerd
You need to find the acceleration. They're both hanging down, right?

Summation of forces = force of block 1 minus force of block 2 (since they're acting in separate directions)
(and be sure to remember, then, that your acceleration will be in the direction of block 1's force if it's the positive one)

Total force = total mass * acceleration

therefore total acceleration = total force / total mass

total force = force 1 - force 2

total mass = mass 1 + mass 2

force of one block = its mass * gravity

(The units of force are kg*m/s^2. Gravity is in m/s^2. You'll never forget formulas if you learn the units and derivation behind them.)

force = mass1*g - mass2*g
(g = 9.8 m/s^2)

force = force
(mass1 * g) - (mass2 * g) = (mass 1 + mass 2) * acceleration

I don't want to do it for you. I might have said too much already.

so with an acceleration of 2.07 and masses of 2.8 and 4.3 the force on the string would be 11.701 N right?