#$&*
Phy 121
Your 'cq_1_12.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_12.1_labelMessages **
Masses of 5 kg and 6 kg are suspended from opposite sides of a light frictionless pulley and are released.
• What will be the net force on the 2-mass system and what will be the magnitude and direction of its acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
Find the force for both weights.
F=m*a
F=6 kg*9.8 m/s^2= 58.8 N
F=5 kg *9.8 m/s^2= 49 N
F_net=58.8N-49N= 9.8 N
So we know the F_net, and the total weight (6kg+5kg=11kg)
@&
That's total mass, not total weight.
Weight is the force exerted on a mass by gravity.
*@
a=F_net/m a=9.8N/(11kg)= 0.89 m/s^2
@&
Good.
*@
@&
*@
@&
However you didn't specify the positive direction, which has the potential to cause an error in the next calculation.
*@
#$&*
• If you give the system a push so that at the instant of release the 5 kg object is descending at 1.8 meters / second, what will be the speed and direction of motion of the 5 kg mass 1 second later?
answer/question/discussion: ->->->->->->->->->->->-> :
Descending=negative (-1.8m/s)
@&
OK, you have specified your directions. Good.
*@
a=0.89 m/s^2 'dt=1 sec
'dv=a*'dt
'dv=0.89m/s^2*1 sec
'dv=0.89 m/s^2
@&
`dv wouldn't have units of m/s^2.
However .89 m/s^2 * 1 sec doesn't have units of m/s^2 either. The units of that product are m/s, which are units of `dv.
*@
vf=-1.8m/s a=0.89 m/s^2
vf=v0+'dv
'dv=-1.8 m/s +(0.89m/s^2)
@&
You cannot add unlike quantities. These quantities are unlike, having different units (m/s vs. m/s^2).
I also believe that this is the solution for vf, not `dv. I suspect that's just a typo.
*@
v0=-0.9 m/s, it still will be descending since it i negative, but at a slower rate, -0.9m/s (vf) rather than -1.8 m/s (v0)
#$&*
• During the first second, are the velocity and acceleration of the system in the same direction or in opposite directions, and does the system slow down or speed up?
answer/question/discussion: ->->->->->->->->->->->-> :
The object is slowing down and velocity and acceleration goes opposite directions (acceleration is positive, and the velocity is negative).
@&
Despite a few glitches, your overall procedure is good and this solution and your interpretation are both correct.
*@
** **
20 minutes
** **
@&
Good solution, but check my notes for some pitfalls, especially regarding units.
*@