Tag: energy and its forms

Questions Related to energy and its forms

An energy of 4 kJ causes a displacement of 64 m in 2.5 s. The power delivered is

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

  1. 16 W

  2. 160 W

  3. 1600 W

  4. 16000 W

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Correct Option: C
Explanation:

Given that


Energy, $E=4\ kJ=4000\ J$
Time taken , $t=2.5\ secs$

Power delivered , $P=\dfrac Et=\dfrac{4000}{2.5}= 1600\ W$

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 

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

  1. $t ^ { 1 / 2 }$

  2. $t ^ { 3 / 2 }$

  3. $t ^ { 5 / 2 }$

  4. $t ^ { 7 / 2 }$

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Correct Option: B
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.

In the above question, if the work done on the system along the curved path $ba$ is $52\ J$, heat absorbed is 

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

  1. $-140\ J$

  2. $-172\ J$

  3. $140\ J$

  4. $172\ J$

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Correct Option: A

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,

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

  1. 5 kg

  2. 0.5 kg

  3. 0.05 kg

  4. 5 gm

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Correct Option: D
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 $5\,gram$

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?

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

  1. $12.4\ kW$

  2. $6.2\ kW$

  3. $24.8\ kW$

  4. $13.77\ kW$

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Correct Option: A

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

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

  1. 2 amp

  2. 4 amp

  3. 6 amp

  4. 8 amp

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Correct Option: B
Explanation:

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

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

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

  1. $50$

  2. $5000$

  3. $100$

  4. $980$

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Correct Option: D
Explanation:

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


Hence correct answer is option $D $ 

A tap supplies water at 22C. A man takes 11 litre water per minute at 37C from the geyser. The power of geyser is

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

  1. 525 W

  2. 1050 W

  3. 1575 W

  4. 2100 W

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Correct Option: B

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, $(g=10ms^{-1})$

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

  1. $2880\ kJ$

  2. $1440\ kJ$

  3. $3800\ kJ$

  4. $720\ kJ$

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Correct Option: B
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=$72\times 10^4(3-1)=1440 kJ$

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 $\mu$

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

  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 } $

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Correct Option: B