Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics heat engine: second law of thermodynamics conversion of heat into work: heat engine and it's efficiency engines and cycles heat engines refrigerators and heat pumps

An engine has an efficiency of 0.25 when temperature of sink is reduced by 58C,if its efficiency is doubled, then the temperature of the source is:

  1. 150K

  2. 222K

  3. 242K

  4. 232K
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let us consider $T _1=$ temperature of the source

$T _2=$ temperature of the sink
The efficiency of the engine,
$0.25=1-\dfrac{T _2}{T _1}$
$\dfrac{T _2}{T _1}=0.75$
$T _2=0.75T _1$. . . . . . . . .(1)
When the temperature of the sink is reduced by $58^0C$, then the efficiency is double,
$2\times 0.25=1-\dfrac{T _2-58}{T _1}$
$\dfrac{T _2-58}{T _1}=0.5$
$T _2-58=0.5T _1$
$0.75T _1-58=0.5T _1$ .........(from equation 1)
$0.25T _1-58=0$
$0.25T _1=58$
$T _1=\dfrac{58}{0.25}$
$T _1=232 K$
The correct option is D.

Multiple choice physics kirchhoff's law combination of resistors combination of cells combinations of components

The diagram shows a $40\Omega$ resistor and a $60\Omega$ resistor connected in parallel.
What is the total resistance between points P and Q?

  1. less than $40\Omega$

  2. $50\Omega$

  3. between $50\Omega$ and $100\Omega$

  4. $100\Omega$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
For parallel connection
$R _{eq}= \dfrac{R _1 \times R _2}{R _1 +R _2}$
$\implies R _{eq}= \dfrac{40 \times 60}{40+60}$
$\implies R _{eq}= 24 \Omega$

So, it is less than $40 \Omega$
Multiple choice relativistic mechanics option a: relativity physics

Radiation with energy that is easily detected as quanta _______________.

  1. $1$ eV

  2. $1$ KeV

  3. $1$ MeV

  4. $10^{-10}$ eV
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Radiation with energy in the MeV range (gamma rays) is typically detected as discrete quanta using devices like scintillation counters. Lower energies are often treated as waves or are harder to detect as individual quanta in standard laboratory settings.

Multiple choice relativistic mechanics option a: relativity physics

Two masses of 1g and 4g are moving with equal K.E. The ratio of the magnitude of their linear momentum is-

  1. 1 : 1

  2. 1 : 2

  3. 1 : 3

  4. 1 : 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Kinetic energy K = p^2 / (2m), so momentum p = sqrt(2mK). Since K is equal for both, the ratio of momenta p1/p2 = sqrt(m1/m2) = sqrt(1/4) = 1/2.

Multiple choice relativistic mechanics option a: relativity physics

Length contraction happens only __________________.

  1. perpendicular to direction of motion

  2. along direction of motion

  3. both a and b

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the theory of special relativity, length contraction occurs only in the direction of the relative motion between the observer and the object.

Multiple choice relativistic mechanics option a: relativity physics

If a constant force acts on a particle, its acceleration will

  1. remain constant

  2. gradually decrease

  3. gradually increase

  4. be undefined
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Acceleration happens because there is force applied to the object, if the force is constant, we have constant acceleration.
Multiple choice relativistic mechanics option a: relativity physics

As the speed of a particle increases, its rest mass

  1. increases

  2. decreases

  3. remains the same

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

Rest mass $(m _o)$ is defined as the mass of the object at rest (or in rest frame) which remains constant.

Only the mass of the moving object changes as the speed increases  via   $m  = \dfrac{m _o}{\sqrt{1-\dfrac{v^2}{c^2}}}$
Hence option C is correct.

Multiple choice relativistic mechanics option a: relativity physics

If $M$ and $m$ are moving mass and rest mass respectively of a body and $c$ is speed of light,

then kinetic energy of body is given by :

  1. $K = [m - M]c^2$

  2. $K = [M - m]c^2$

  3. $K = Mc^2$

  4. $K = mc^2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Kinetic energy in relativistic mechanics is the difference between total energy (Mc^2) and rest energy (mc^2), which simplifies to (M - m)c^2.

Multiple choice relativistic mechanics option a: relativity physics

A person is watching a rocket with an astronaut inside move by at a speed near the speed of light.
Which of the following statements is true?

  1. The mass of the rocket is greater from the person's perspective than from the astronaut's perspective

  2. The mass of the rocket is the same from the perspective of the person and the astronaut

  3. The mass of the rocket is greater from the perspective of the astronaut than from the perspective of the person

  4. The person's mass is greater, from his own perspective, as the rocket flies by, than it was before the rocket flew by

  5. The astronaut's mass is greater, from his own perspective, as he flies by the person, than it was before he flew by the person
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mass of the moving object as seen by the person in rest frame,  $m = \dfrac{m _o}{\sqrt{1-v^2/c^2}}$  $\implies m>m _o$

where  $m _o$ is the rest mass as seen by the astronaut in moving frame. 
Thus mass of rocket would be greater from the person's perspective than from the astronaut's perspective.

Multiple choice relativistic mechanics option a: relativity physics

A man flies past a woman at a speed near the speed of light. What might correctly be said by whom as the man flies by? Assume that neither the man nor the woman usually travels so fast relative to other near-by objects

  1. The man could say, "I am more massive than usual"

  2. The man could say, "Time is passing more slowly for me the usual"

  3. The woman could say to the man, "You are more massive than usual"

  4. The woman could say to the man, " You are wider than usual"

  5. The woman could say, "Time is passing more quickly for me than usual"
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mass of the moving man as seen by the woman in rest frame           $m = \dfrac{m _o}{\sqrt{1-v^2/c^2}}$      $\implies m>m _o$

where  $m _o$ is the rest mass of the man. 
Thus according to the woman, the man seems to be more massive than usual.