Tag: physics

Questions Related to physics

A straight rod of length L has one of its ends at the origin and the other at $x=L$. If the mass per unit length of the rod is given by Ax where A is constant, where is its mass centre?

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. $L/3$

  2. $L/2$

  3. $2L/3$

  4. $3L/4$

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Correct Option: B
Explanation:
I assume you meant to say "a is a CONSTANT".

xc = coordinate of center of mass

M = total mass

$xc = ∫xdm / ∫dm = ∫xdm / M$

Given:$ m(x) = ax ⇒ dm/dx = a ⇒ dm = adx$

$∫xdm = ∫01 x(adx) = a/2$

$M = ∫dm = ∫(dm/dx)dx = ∫01 adx = a$

$xc = (a/2)/a = 1/2$

By the way, this is a mechanics problem (in statics), not a thermodynamics problem.

 

A circular disc of radius R is removed from a bigger circular disc of radius 2R such that the circumferences of the discs coincide. The centre of mass of the new disc is $\alpha R$ fromthe centre of the bigger disc. The value of $\alpha$ is

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. $\cfrac{1}{2}$

  2. $\cfrac{1}{6}$

  3. $\cfrac{1}{4}$

  4. $\cfrac{1}{3}$

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Correct Option: D

Force acting per unit area is

physics statics and dynamics of fluid (liquid and gas) pressure in liquids and gases pressure dependence on force and area concept of pressure

  1. Acceleration

  2. Pressure

  3. Velocity 

  4. None

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Correct Option: B
Explanation:

Pressure is defined as force per unit area. The standard unit for pressure is the Pascal, which is a Newton per square meter.

$P=\dfrac{F}{A}$

For an object sitting on a surface, the force pressing on the surface is the weight of the object, but in different orientations it might have a different area in contact with the surface and therefore exert a different pressure.

The pressure of the fluid acting sideways is known as its lateral pressure

physics statics and dynamics of fluid (liquid and gas) pressure in liquids and gases pressure dependence on force and area concept of pressure

  1. True

  2. False

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Correct Option: A
Explanation:

pressure acting sideways is known as lateral pressure .

so option (A) is correct

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

Show answer
Correct Option: B
Explanation:

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