- AThe angular acceleration of the rod will be .
- BThe normal reaction force from the floor on the rod will be .
- CThe radial acceleration of the rod's center of mass will be .
- DThe angular speed of the rod will be .
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Correct answer: B, C, D
- Model the motion
Since the floor has large friction, the lower end of the rod does not slip. So the rod rotates about the contact point with the floor as a fixed pivot.
For a uniform rod of length pivoted at one end:
- Moment of inertia about the pivot:
- Distance of center of mass from pivot:
Let be the angle the rod makes with the vertical. We are asked for .
- Angular speed using energy conservation
Initially, the rod is vertical and at rest.
When the rod makes angle with the vertical, the center of mass has fallen by
Loss in gravitational potential energy = gain in rotational kinetic energy:
Substitute :
At , :
So,
Therefore, Option D is correct.
- Angular acceleration
Torque of gravity about the pivot is
Using :
At :
This is not equal to .
Therefore, Option A is incorrect.
- Radial acceleration of the center of mass
For rotation about a fixed point, radial (centripetal) acceleration of the center of mass is
Using :
Therefore, Option C is correct.
- Normal reaction from the floor
Let us find acceleration of the center of mass in vertical direction.
For a rod making angle with vertical, taking pivot as origin,
Differentiate twice:
At :
So,
Now apply Newton's second law in vertical direction:
Therefore, Option B is correct.
- Final evaluation of options
- A: Incorrect
- B: Correct
- C: Correct
- D: Correct
So the correct choices are:
- Comparison with stored correct answer
Stored correct answer: B, C, D
My derived answer: B, C, D
They match exactly.
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