System of Particles and Rotational Motion - Result Question 2

2. Which of the following statements are correct?

[2017]

(A) Centre of mass of a body always coincides with the centre of gravity of the body

(B) Centre of mass of a body is the point at which the total gravitational torque on the body is zero

(C) A couple on a body produce both translational and rotation motion in a body

(D) Mechanical advantage greater than one means that small effort can be used to lift a large load

(a) (A) and (B)

(b) (B) and (C)

(c) (C) and (D)

(d) (B) and (D)

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Answer:

Correct Answer: 2. (d)

Solution:

  1. (d) Mechanical advantage, M. A. $=\frac{\text{ Load }}{\text{ Effort }}$

If M.A. > $1 \Rightarrow$ Load > Effort

Centre of mass may or may not coincide with centre of gravity. Net torque of gravitational pull is zero about centre of mass.

$ \tau_g=\Sigma \tau_i=\Sigma r_i \times m _{i g}=0 $