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)
Show Answer
Answer:
Correct Answer: 2. (d)
Solution:
- (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 $
