- A
- B
- C
- D
View written solutionFree
Correct answer: D
- Given data
- Mass of stick:
- Length of stick:
- Angle with wall:
- Therefore angle with floor:
- Wall is smooth, so wall reaction is the only force at contact with wall.
- This reaction is perpendicular to the stick.
- Reaction of wall and reaction of floor have equal magnitudes.
- Weight of stick:
- Forces acting on the stick
Let:
- Wall reaction =
- Floor normal reaction =
- Friction at floor =
Since the stick makes with the floor, a force perpendicular to the stick makes angle with +x axis, so components of wall reaction are:
Thus wall reaction has:
- leftward component
- upward component
At the floor:
- normal reaction upward
- friction rightward (to balance leftward push of wall)
- Translational equilibrium
Horizontal equilibrium
Vertical equilibrium
Given magnitudes of floor reaction and wall reaction are equal.
The resultant reaction at floor is:
Condition:
Squaring:
Using :
Now from vertical equilibrium:
Hence
and friction
So
This does not match any option yet, so we must carefully interpret the wall reaction direction.
- Correct geometric interpretation of wall reaction
The wall is smooth and vertical, but the stick touches the top edge of the wall, not the vertical face alone. Since the statement says reaction is perpendicular to the stick, the contact is effectively at the top corner of the wall, and the reaction acts normal to stick.
Let the bottom end be at floor, and contact point with top of wall be at height .
Take bottom point as pivot.
The stick makes with floor. If the contact point is at height , then distance along stick from bottom to contact point is:
The center of mass is at midpoint of stick, i.e. at distance from bottom.
- Torque equilibrium about bottom end
Since wall reaction is perpendicular to stick and applied at distance along the stick, its torque magnitude is:
Weight acts vertically downward at center. Its horizontal distance from bottom is:
So torque due to weight is:
Equilibrium gives:
- Now use force balance with equality of reactions
Let wall reaction be perpendicular to stick and directed up-left. Then:
Floor reaction magnitude equals wall reaction:
So
Then Rightarrow R_w=16,\text{N}$$
Thus
Again this does not fit options. Therefore the intended condition is likely that the normal reaction at floor equals wall reaction, i.e.
Then from vertical equilibrium:
Hence friction:
This matches the options.
- Find from torque balance
Using
Substitute :
- Final answer
So the correct option is D.
- Comparison with stored correct answer
Stored correct answer: D
Our derived answer: D
They agree.
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