# Rotational motion (easy)

1. Nov 17, 2007

### noapologies01

fig. MC2 shows a uniform 100-cm long bar of weight F w, balanced in equilibrium on a frictionless pivot. [picture a long bar and it being balanced on the point, but the point is towards the beginning of the bar with a weight to the left of it, to keep it at equilibrium]
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(w) ^
l l
L J

Q: what is the value of the upward reaction force on the bar at the pivot?
a. F w
b. 2F w
c. 3F w
d. 4F w

F w(weight)

Q2: what is the value of the load hanging at the left of pivot?
a. F w
b. 2F w
c. 3F w
d. 4F w

no clue how they got the numbers in front of the Fw

2. Nov 17, 2007

### rl.bhat

Weight of the bar always acts at the center of the rod. Consider the pivot at a distance x from the center of the rod. The other end of the rod will be at 50 - x from the pivot. Now apply the law moments about the pivot and find the wight at the left end of the rod and reaction on the pivot.

3. Nov 17, 2007

### noapologies01

4. Nov 17, 2007

### rl.bhat

The body remains in equilibrium when clockwise moment= anticlockwise moment. Hence F*X = F1*(50-X). To solve the problem you must know the position of the pivot. Is it indicated in the figure?

5. Nov 17, 2007

### noapologies01

it just shows a long bar and almost all the way to the left of it theres a weight and next to the weight is whatever its called holding up the long bar..if u got an email address i can send u a pic

6. Nov 17, 2007

### rl.bhat

7. Nov 17, 2007

### noapologies01

8. Nov 18, 2007

### rl.bhat

Got your e-mail. I asked you to send the exact diagram. In the question some data is missing. The attachment was so large that I closed it before it completed. I saw your other quote. In that also sufficient data is not provided. In both the problems you have not shown your work.
a picture shows the 2 hanging objects on one side is heavier than the clay(which is high in the air).. Where is the picture? Unless we know the exact position of the pivot we can,t solve the proble. In both the problems you have to use simple laws of moments which you can get in any PHYSICS BOOK.

Last edited: Nov 18, 2007
9. Nov 18, 2007

### noapologies01

i know buyt my physics book doesnt explain it very well..ill try sending it to u again..i dont ask for help if im able to solve it myself, but i cant