Question

An automobile is moving at 100kmph and its engine is exerting an attractive force of 3920 N. Find power.
A. 108.8 hp
B. 146 hp
C. 195 hp
D. 0 hp

Answer 1

Hint:In physics, the concept of work and energy is thoroughly correlated and linked to force. It is because whenever force is applied to any object, there is some work done and also some change in the energy. Work is a physical activity that includes movement in the direction of applied force. But when this work is calculated per unit time then this is termed as power.

Complete step by step answer:
Power is a scale that measures the speed for completing work. Therefore, power is how quickly one can complete work. In essence, it refers to the consumption of energy per unit time. Any object that transfers higher energy in a limited time can be termed to possess greater power. The SI unit of energy is Watts, which is Joules/second.
We know that power is given by:
$P = F \times v$
We will now substitute $F=3920 N$, $v=100kmph$ to find the value of P.
$\Rightarrow P = 3920\;N \times 100\;kmph \times \dfrac{{\left( {5/18} \right)\;m/s}}{{1\;kmph}}\\$
$\Rightarrow P = 108888\;W \times \dfrac{{1\;hp}}{{746\;W}}\\$
$\Rightarrow P = 145.9\;hp$

Therefore, the power is 145.9 hp.This is nearly equal to 146hp. Hence option (B) is correct.

Additional Information: Energy and power are two terms that people often use interchangeably in daily life. However, when dealing with Physics, both of these differ in definition, scope and many other factors. Thus, understanding the difference between power and energy is crucial.

Note:Whenever we come up with this type of problem where we are asked to find the unit of any quantity. Then we first write the formula to calculate that quantity and then in place of values we put the unit of every quantity. After solving that we will get the required S.I. unit asked for that quantity (here power).