MHT CET · Physics · Center of Mass Momentum and Collision

A metal rod of weight ' \(W\) ' is supported by two parallel knife-edges \(A\) and \(B\). The rod is. in equilibrium in horizontal position. The distance between two knife-edges is ' \(r\) '. The centre of mass of the rod is at a distance ' \(x\) ' from A. The normal reaction on A is

A \(\frac{\mathrm{W} \cdot \mathrm{r}}{\mathrm{x}}\)
B \(\frac{\mathrm{W} \cdot \mathrm{x}}{\mathrm{r}}\)
C \(\frac{W \cdot(r-x)}{x}\)
D \(\frac{\mathrm{W} \cdot(\mathrm{r}-\mathrm{x})}{\mathrm{r}}\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{\mathrm{W} \cdot(\mathrm{r}-\mathrm{x})}{\mathrm{r}}\)

Step-by-step Solution

Detailed explanation

For equilibrium,
\(\begin{aligned}& \mathrm{N}_1 \mathrm{r}=\mathrm{W}(\mathrm{r}-\mathrm{x}) \\\therefore \quad & \mathrm{N}_1=\frac{\mathrm{W}(\mathrm{r}-\mathrm{x})}{\mathrm{r}}\end{aligned}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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