A rotor weighing 2 kN is supported on bearings A and B which are 1 m apart. The centre of mass of the rotor is at a distance 0.4 m from bearing A. It is observed that there is an unbalanced couple of magnitude 300 N-m which leaves the shaft balanced statically. The dynamic reactions at the supports will be

This question was previously asked in
ESE Mechanical 2016 Paper 2: Official Paper
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  1. 800 N and 800 N
  2. 300 N and 800 N
  3. 800 N and -300 N
  4. 300 N and -300 N

Answer (Detailed Solution Below)

Option 4 : 300 N and -300 N
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Detailed Solution

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Concept:

The dynamic reaction is due to the unbalanced couple, the static reaction is due to the weight of the shaft.

The dynamic reaction due to the couple on the shaft will be equal and opposite of each other.

This reaction is given by

\(R = \pm \frac{C}{L}\)

Where R is the reaction and C is the unbalanced couple and L is the length between the supports.

Calculation:

F1 M.J 24.4.2 pallavi D3

Given that the unbalanced couple magnitude is 300 N-m

∴ Reactions will be \(R = \; \pm \frac{{300\;N - m}}{{1\;m}} = \; \pm \;300\;N\)

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