Tag: work and power

Quizzes (3) Questions (84)

Questions Related to work and power

Multiple choice power work and power energy and its forms work, energy and power physics

If the heart pushes 1 cc of blood in one second under pressure of 20000$Nm^{-2}$, the power of heart is

  1. 0.02 W

  2. 400 W
  3. $5\times 10^{-10}W$

  4. 0.2 W
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given,

$P=20000Nm^{-2}$
$\dfrac{dV}{dt}=1cc/s$
Power, $P=\dfrac{W}{t}=F.v=PA\dfrac{dx}{dt}$   (as, $F=PA$)
$P=P.\dfrac{dV}{dt}$
$P=20\times 10^3\times \dfrac{1}{(10^2)^3}$
$P=\dfrac{2}{100}=0.02W$
The correct option is A.

Multiple choice power work and power energy and its forms work, energy and power physics

A pump can hoist 9000 kg of coal per hour from a mine of 120 m deep. calculate the power of the pump, in watts, assuming its efficiency is 75%, g=9.8 $m/s^{2}$

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = mgh = 9000 kg * 9.8 m/s^2 * 120 m = 10,584,000 J. Power = Work / time = 10,584,000 J / 3600 s = 2940 W. Given 75% efficiency, the required power input is 2940 / 0.75 = 3920 W.

Multiple choice power work and power energy and its forms work, energy and power physics

A man starts walking from a point on the surface of earth (assumed smooth) and reaches diagonally opposite point. What is the work done by him? 

  1. Zero

  2. Positive

  3. Negative

  4. Nothing can be said
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If we consider work done against gravity, walking from one point to the antipodal point involves moving away from Earth's center then descending back down. The net work against gravity is zero (positive climbing cancels negative descending). However, the question is poorly specified as the person does positive muscular work throughout.

Multiple choice power work and power energy and its forms work, energy and power physics

The power of water pump is 4 kW. If g = 10 $ms^{-2}$, the amount of water it can raise in 1 minute to a height of 20 m is 

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power = 4000 W. Time = 60 s. Work = Power * time = 240,000 J. Work = mgh -> 240,000 = m * 10 * 20 -> 240,000 = 200m -> m = 1200 kg. Since 1 kg of water = 1 liter, the volume is 1200 liters.