System of Particles and Rotational Motion - Result Question 27

27. A force F=αi^+3j^+6k^ is acting at a point r=2i^6j^12k^. The value of α for which angular momentum about origin is conserved is :

[2015 RS]

(a) 2

(b) zero

(c) 1

(d) -1

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Answer:

Correct Answer: 27. (d)

Solution:

  1. (d) From Newton’s second law for rotational motion,

τ=dLdt, if L= constant then τ=0

So, τ=r×F=0

(2i^6j^12k^)×(αi^+3j^+6k^)=0

Solving we get α=1



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