Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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?

  1. $L/3$
  2. $L/2$
  3. $2L/3$
  4. $3L/4$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

 

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

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

  1. $\cfrac{1}{2}$
  2. $\cfrac{1}{6}$
  3. $\cfrac{1}{4}$
  4. $\cfrac{1}{3}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using the negative mass method, the center of mass of the remaining part is found by subtracting the mass and moment of the smaller disc from the larger one. The calculation leads to alpha = 1/3.

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

Force acting per unit area is

  1. Acceleration

  2. Pressure

  3. Velocity

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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, $I = \displaystyle\frac{880}{220} = 4  amp$.