Posted by Physics on .
I got two questions
Three blocks on a fricitonless horizontal surface are in contact with each other
a force F is applied to block 1 mass m1
Draw a free body diagram for each block
ok done
the accelration of the system (in terms of m1, m2, and m3)
ok done I got
a = (m1 + m2 + m3)^1 (force F)
the force of contact that each block exerts on its neighbor
ok no idea how to do this
>Force F  m1 >contact force  m2 >contact force  m3 
ok so how do i do this
ok and
a block (mass m1) on a smooth horizontal surface, connected by a thin cord that passes over a pulley to a second block (m2), which hangs vertically.
Draw a free body diagram for each block showing the force of gravity on each, the force (tension) exerted by the cord, and any normal force
ok done
determine formulas for the acceleration of the system and for the tnesion in the cord. Ignore friction and the masses of the pulley and cord
ok well isn't the force of tension just the opposite in direction but equal in magntiude of the force of gravity on second hanging block?
Also isn't the accleeration zero???
Isn't the net force zero???
ok i do not know how to find the acceleration of the system

Physics 
Physics,
Ok I guess I'm drawing the free body diagram wrong how do I draw it because this is not making much sense to me

Physics 
drwls,
Why did you start this question by reasking the three blocks question that we have already explained to you? I assume that you followed directions and are through with that one.
As for the problem with the two masses, cord and pulley: the acceleration is NOT zero in a frictionless situation. The dangling mass m2 exerts a weight force on the cord, which allows both masses to move with the same acceleration, a. What equations of motion have you derived from your FBDs?
The tension force T in the cord does not equal the weight force W = m2*g when the masses are accelerating.
You should have two equations in two unknowns: T and a.
T = m1*a
m2*g  T = m2*a
m2*g = (m1 + m2) a
Solve for a and T 
Physics 
Physics,
is this right?
Force F onto m1>m1 contact force onto m2>m2contact force onto m3>m3 
Physics 
drwls,
No, it is not right. Force and mass have different dimensions.
Mass has to be multiplied by an acceleration rate to get force.