Question

SI unit of moment of force is
A. Dyne-cm
B. Erg-kg
C. Newton-meter
D. Newton-kg

Answer 1

Units and Dimensions play key roles in physics. Various quantities have various units. SI units of the main fundamental quantities are kilogram for mass while meter for length second for time kelvin for temperature while ampere for the current. By using these units we will solve this question.

Formula used:
$\tau = \mathop r\limits^ \to \times \mathop F\limits^ \to$

Complete step by step answer:
It's known that there are various languages in this world. Same feelings are expressed in different languages using different terms. But when we measure a certain quantity of a body let it be mass or length or volume it remains constant wherever we go in this world. Hence scientists had thought that there should be common units to measure these quantities which will be acceptable and understood all over the world without any difficulties. Those units are called SI units or international systems of units. Meter is the SI unit of the length. For mass its kilogram and for time its second.
Now there is another system of units. This is called the CGS system. Here mass is measured in grams and length is measured in centimeters and time is measured in seconds.
The quantity we were given was a moment of force. Moment of force means torque. Torque is the cross product of perpendicular distance from the axis about which we measure torque and the force we apply.
So
$\tau = \mathop r\limits^ \to \times \mathop F\limits^ \to$
SI unit of distance is meter and of force is newton.
\eqalign{ & \tau = \left( {{\text{meter}}} \right)({\text{newton)}} \cr & \tau = {\text{Newton - meter}} \cr}
Hence option C is correct.

Note:
The unit of force is newton and it can also be expressed in terms of kilogram and meter and second. One newton will be equal to 1 kg meter per second square. Just like we multiply the physical quantities, we can apply the same rules to multiply units or dimensions. Some quantities don’t have the dimensions.