Question

(i) Name the physical quantity measured in terms of horse power.
(ii) A nut is opened by a wrench of length if the least force required is, find the moment of force needed to loosen the nut.
(iii) Explain briefly why the work done by a fielder when he takes a catch in a cricket match is negative.

Answer 1

Hint:(i) If we see, the name itself gives us an idea that physical quantity will be power.
(ii) Force is applied at the end of the wrench near the nut so the moment of force will be its length into least force required.
(iii) When we do work in direction opposite to its displacement, it becomes negative work.

Complete step by step answer:
(i)Power is the physical quantity which is measured in horsepower.
In SI unit conversion following formula is used
$1$Horse power \[ = 746\]watts
(ii)Moment of force \[ = r \times F\]
Here, \[F = 2N\]
\[r = 20{\text{ }}cm{\text{ }}or{\text{ }}0.2\;m\]
So, moment of force comes out to be \[2 \times 0.2{\text{ }}m = 0.4{\text{ }}N\]
(iii)Force applied by the fielder on the ball is in the opposite direction of displacement of ball.
The ball is displaced in downwards direction and when the fielder catches it, he applies force in upward direction. So, work done by the fielder on the ball while taking catches is negative.

Note: Commercially, the popular unit of electrical power is Horsepower (HP). All the electrical motors are preferably specified with respect to their horse power. Do remember to convert cm into SI unit, m. Sometimes work done can also be zero, for example, work done by a person carrying a bag on his head and moving.