Tag: physics

Questions Related to physics

State whether true or false.
The mass of a body can never be zero.

physics measurement of physical quantities kinds of units fundamental quantities standardized measurement

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
Mass of a body is defined as the quantity of matter contained in it. Since, all bodies are made up of certain matter. Thus mass of body can never be zero.

Which one of the following is not a fundamental SI unit?

physics measurement of physical quantities kinds of units fundamental quantities standardized measurement

  1. Ampere

  2. Candela

  3. Newton

  4. Kelvin

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Correct Option: C
Explanation:

F = ma = kgms-2

SI unit of force is Newton(W)

Hence, newton is a derived unit

A dimensionless quantity

physics measurement of physical quantities kinds of units fundamental quantities standardized measurement

  1. never has a unit

  2. always has unit

  3. may have a unit

  4. does not exit

Show answer
Correct Option: C
Explanation:

A dimensionless quantity is that is always independent of basic $7$ units:-meter, second, kilogram, Kelvin, Candela, ampere.

But it is not necessary. A dimensionless quantity is unitless. And eg, for this, is radian (unit of angle), which is dimensionless quantity because it is the ratio of two lengths.

Some physical quantities are given in Column I and some possible SI units in which these quantities may be expressed are given in Column II. Match the physical quantities in Column I with the units in Column II.

Column I Column II
i. $GM _eM _s$ a. (volt) (coulomb) (metre)
ii. $3RT/M$ b. $(kilogram)(metre)^3 (second)^2$
iii. $F^2/q^2B^2$ c. $(meter)^2 (second)^{-2}$
iv. $GM _e/R _e$ d. $(farad) (volt)^2 (kg)^{-1}$


where G is universal gravitational constant; $M _e$ mass of the earth; $M _s$, mass of sun; $R _e$ radius of the earth; R, universal gas constant;T, absolute temperature; M, molar mass, F, force; q, charge; B, magnetic field.

physics measurements and units kinds of units fundamental quantities standardized measurement

  1. $i \rightarrow b., ii \rightarrow c.,d., iii \rightarrow c.,d., iv \rightarrow c.,d.,$

  2. $i \rightarrow a., ii \rightarrow c.,d., iii \rightarrow c.,d., iv \rightarrow c.,d.,$

  3. $i \rightarrow d., ii \rightarrow c.,d., iii \rightarrow c.,d., iv \rightarrow c.,d.,$

  4. $i \rightarrow c., ii \rightarrow c.,b., iii \rightarrow c.,d., iv \rightarrow c.,d.,$

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Correct Option: B

Pressure (P), density $\displaystyle (\rho )$ and velocity (V) be taken as fundamental quantities for dimensional analysis.

physics measurement of physical quantities kinds of units fundamental quantities standardized measurement

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
Pressure is calculated as   $P = \dfrac{Force}{Area}$
Density  $\rho = \dfrac{Mass}{Volume}$

Velocity  $V = \dfrac{Displacement}{time}$

So, pressure, density and velocity are derived from other quantities and so, these are termed as derived quantities , not fundamental quantities.
Hence, the given statement is false.

A 50.0 kg boy is sitting on an amusement park ride where he accelerates straight upward from rest to a speed 30.0 m/s in 3.0 s. What is his mass as he accelerates upward?

physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

  1. 990.0 kg

  2. 100.0 kg

  3. 50.0 kg

  4. 5.00 kg

  5. 0 kg

Show answer
Correct Option: C
Explanation:

Mass of an object always remains constant whether the object is accelerating or not. Apparent weight of the object changes due to acceleration.

Hence the mass of the boy is $50$ kg even he accelerates upward.
Thus option C is correct.

A plumb bob is hung from the ceiling of a train compartment. the train moves on an inclined track of inclination $30^\circ $ with horizntal. The acceleration of train up the plane is $a=\,g/2$. The angle which the string supporting the bob makes with normal to the ceiling in equilibrium is-

physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

  1. $30^\circ $

  2. ${\tan ^{ - 1}}\left( {2/\sqrt 3 } \right)$

  3. ${\tan ^{ - 1}}\left( {\sqrt 3/2 } \right)$

  4. ${\tan ^{ - 1}}\left( 2 \right)$

Show answer
Correct Option: C

A man of mass 'm' stands on a weighing machine in a lift

List - I  List-II
(a) Lift moves up with uniform acceleration a  (d) mg
(b) Lift moves down with uniform acceleration a (e) m(g$+$a)
(c) Lift moves down with uniform velocity (f) m(g-a)
physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

  1. $a\rightarrow e,b\rightarrow f,c\rightarrow d,$

  2. $a\rightarrow d,b\rightarrow f,c\rightarrow e,$

  3. $a\rightarrow d,b\rightarrow e,c\rightarrow f,$

  4. $a\rightarrow f,b\rightarrow d,c\rightarrow e,$

Show answer
Correct Option: A
Explanation:

When the lift moves $UP$ with uniform acceleration $a$ $Pseudo$ force on the man is $ma$ downward.

Net downward force is $mg+ma$. Hence, $e$

When the lift moves $down$ with uniform acceleration $a$ $Pseudo$ force on the man is $ma$ upward.
Net downward force is $mg+ma$. Hence, $f$


When the lift moves down with $uniform \ velocity$, only force acting is gravity.

Hence net force on man is $mg$. Hence, $d$

A passenger in a train hangs a stone from a string and holds it vertically. It is observed that the string is vertical as seen from the man.
Which of the following could be true about the motion of the train?
I. The train is at rest.
II. The train is moving with a constant velocity.
III. The train is increasing its speed.
IV. The train is decreasing its speed.

physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

  1. I only

  2. III only

  3. I or II, but not III or IV

  4. III or IV, but not I or II

  5. IV only

Show answer
Correct Option: C
Explanation:

When the train is either at rest or moving with constant velocity, then the acceleration of the train is zero and hence there is no pseudo force acting on the stone in the horizontal direction which makes the string tied to the stone to stay in vertical direction.

If the train either increases or decreases its speed, then the stone experiences a pseudo force in the horizontal direction due the acceleration of train and thus the string gets tilted by some angle with the vertical direction. 
Thus option C is correct.

When a car accelerates rapidly forward, the heads of people in the car seem to jerk backward.
This is best explained by which of the following?

physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

  1. The action is the car accelerating forward; the reaction is the heads accelerating backward

  2. Large forward velocities cause large backward accelerations

  3. The inertia of people's heads is not as big as the inertia of the car

  4. The people's heads initially have no force to accelerate them forward. The heads momentarily remain at rest until the necks and /or head rests apply forward forces to the heads to accelerated then forward

  5. The forward momentum of the car results in an equal backward momentum of the people's head to conserve momentum

Show answer
Correct Option: C
Explanation:

This happens due to inertia of rest . initially both car and people are in rest , when car accelerates rapidly , feet of the people also accelerates with car because they are in contact with the floor of car , but heads of the people do not accelerates quickly because they want to be in rest due inertia of rest therefore people feel a jerk .