Tag: energy and its forms

Quizzes (9) Questions (123)

Questions Related to energy and its forms

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

A constant power is delivered to a body moving along a straight line. the distance travelled by the body in time t is proportional to 

  1. $t ^ { 1 / 2 }$
  2. $t ^ { 3 / 2 }$
  3. $t ^ { 5 / 2 }$
  4. $t ^ { 7 / 2 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} power\, P\, =Fv=mav \ acceleration\, a=\frac { S }{ { { t^{ 2 } } } } \, and\, velocity\, v=\frac { S }{ t } , \ where\, \, S\, \, is\, the\, dis\tan  ce\, moved \ Since\, \, the\, power\, P\, and\, mass\, m\, are\, cons\tan  t,\, we\, \, get \ P=\frac { { mS } }{ { { t^{ 2 } } } } \times \frac { S }{ t } \to { S^{ 2 } }={ t^{ 2 } }\to S\propto { t^{ \frac { 3 }{ 2 }  } } \end{array}$

Hence,
option $B$ is correct answer.

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

A machine gun fires 360 bullets per minute. Each bullet moves with a  velocity of 600 ms$^{-1}$. If the power of the gun is 5.4 kw, the mass of each bullet is,

  1. 5 kg

  2. 0.5 kg

  3. 0.05 kg

  4. 5 gm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given,

Number of bullets, $n=360\,nos.$

Mass of bullet, $m$

Power, $=5400watt$

Kinetic energy of 360 bullets, $K.E=n\times \dfrac{1}{2}m{{v}^{2}}=360\times \dfrac{1}{2}\times m\times {{600}^{2}}=648\times {{10}^{5}}m\,\,J$

$ Power=\dfrac{kineticenergy}{time} $

$ 5400=\dfrac{648\times {{10}^{5}}m}{60} $

$ m=5\times {{10}^{-3\,}}kg\,=\,5\,gram\, $

Hence, weight of each bullet is $5\,gram$

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

The driving side belt has a tension of $1600\ N$ and the slack side has $500\ N$ tension. The belt turns a pulley $40\ cm$ in radius at a rate of $300\ rpm$. The pulley drives a dynamic having $90\%$ efficiency. How many kilowatt are being delivered by the dynamo?

  1. $12.4\ kW$
  2. $6.2\ kW$
  3. $24.8\ kW$
  4. $13.77\ kW$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Power = (T1 - T2) * v. v = omega * r = (2 * pi * 300 / 60) * 0.4 = 12.56 m/s. Power = (1600 - 500) * 12.56 = 13816 W = 13.8 kW. Applying 90% efficiency: 13.8 * 0.9 = 12.42 kW.

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

A heating unit on an electric stove is rated at $880  W$. It is connected to a power supply of $220  V$. The current it will consume is

  1. 2 amp

  2. 4 amp

  3. 6 amp

  4. 8 amp
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Power $= V \times I$
or, $880 = 220 \times I$
or, $I = \displaystyle\frac{880}{220} = 4  amp$.

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

The average power required to lift a $100kg$ mass through a height of $50$ metres in approximately $50$ seconds would be ( in J/s)

  1. $50$
  2. $5000$
  3. $100$
  4. $980$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$Power= Work/Time= F.s/t=mgs/t=(100\times 9.8\times 50)/50= 980W $


Hence correct answer is option $D $ 

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

A rectangular block of dimensions $6m\times 4m\times 2m$ and of density $1.5\ gm/c.c$ is lying on horizontal ground with the face of large area in contact with the ground. The work done in arranging it which its smallest area in contact with a ground is, $(g=10ms^{-1})$

  1. $2880\ kJ$
  2. $1440\ kJ$
  3. $3800\ kJ$
  4. $720\ kJ$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

m=v*density

m=$6\times 4\times 2\times 1.5\times 10^3=72\times 10^3$kg
when face with large area is in contact with the ground its height is 2m
Centre of mass is at a height of 1m

when face with small area is in contact with the ground its height is 6m
Centre of mass is at a height of 3m
W=$72\times 10^4(3-1)=1440 kJ$

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

A small body of mass $m$ is located on a horizontal plane. The body acquires a horizontal velocity ${v} _{0}$. Find mean power developed by the frictional force, during the whole time of its motion. Coefficient of friction is $\mu$

  1. $\cfrac { -\mu mg{ v } _{ 0 } }{ 3 } $
  2. $\cfrac { -\mu mg{ v } _{ 0 } }{ 2 } $
  3. $\cfrac { -\mu mg{ v } _{ 0 } }{ 5 } $
  4. $\cfrac { -\mu mg{ v } _{ 0 } }{ 6 } $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The body decelerates due to friction: a = -mu * g. Final velocity is 0. Time taken t = v0 / (mu * g). Displacement s = v0^2 / (2 * mu * g). Work done = -mu * m * g * s = -m * v0^2 / 2. Mean power = Work / t = (-m * v0^2 / 2) / (v0 / mu * g) = -mu * m * g * v0 / 2.