Question

Which of the following statements are correct?
(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 produces both translational and rotational motion in a body
(d) Mechanical advantage greater than one means that small effort can be used to lift a large load

A. (c) and (d)
B. (b) and (d)
C. (a) and (b)
D. (b) and (c)

Answer 1

This question talks about how the weight of an object acts with respect to the earth and the ratio of load to effort or force applied on an object or load with time.

Complete step by step answer:
Statement 1 is the centre of mass of a body always coincides with the centre of gravity of the body.
Statement 2 is the centre of mass of a body is the point at which the total gravitational torque on the body is zero.
Statement 3 is a couple on a body produces both the translational and rotational motions in a body.
Statement 4 is a mechanical advantage greater than one means that small effort can be used to lift a large load.
Option B is correct, as the two conditions are valid, statement 2 and 4 where centre of mass of a body is the point at which the total or sum of gravitational torque in the body is zero and also where the mechanical advantage (MA) is greater than 1 then which means that small effort applied is required to lift a heavy or large load. The efficiency of the machine with this property can be high.

Note: The above examples can be found as in a small car with a big base where its entire weight concentrates at the centre and also in a funnel that basically faces downwards on the earth with the wide part and the other parts facing up. Center of mass of a body is the average position of all the parts of the system which are weighted according to their masses.