Tag: physics

Questions Related to physics

Which surfaces will reflects most of the light falling on them?

physics reflection of light and shadow regular and irregular reflection regular and diffused reflection laws of reflection

  1. Flat surface

  2. Shiny surface

  3. Smooth surface

  4. Opaque surface

Show answer
Correct Option: B
Explanation:

A perfect smooth and shiny surface will reflect most of the light falling on them.

A bus driver is reversing his bus at a speed $8 m s^{-1}$. The rear view mirror of a bus is a plane mirror. The driver sees in his rear view mirror the image of a car parked behind his bus. The speed at which the image of the car appears to approach the driver will be

physics reflection of light and shadow regular and irregular reflection regular and diffused reflection laws of reflection

  1. $2 m s^{-1}$

  2. $4 m s^{-1}$

  3. $8 m s^{-1}$

  4. $16 m s^{-1}$

Show answer
Correct Option: D
Explanation:

The speed at which the image of the car appears to approach the driver will be $(2 \times 8) m s^{-1} = 16 m s^{-1}$ because rear view mirror is a plane mirror.

Diffused reflection

physics reflection of light and shadow regular and irregular reflection regular and diffused reflection laws of reflection

  1. may produce image

  2. never produce image

  3. must produce image

  4. None of these

Show answer
Correct Option: A

Irregular reflection obeys laws of reflection .

physics reflection of light and shadow regular and irregular reflection regular and diffused reflection laws of reflection

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

All type of reflection obeys laws of reflection.


Given statement is $True$.

Answer-(A)

Reflection from a smooth surface is called __________ reflection.

physics reflection of light and shadow regular and irregular reflection regular and diffused reflection laws of reflection

  1. Regular

  2. Irregular

  3. Multiple

  4. Total internal

Show answer
Correct Option: A
Explanation:
Regular reflection is reflection in which a parallel beam of incident rays is reflected as a parallel beam.

Reflection from smooth surface is regular reflection.

Answer-(A)

The correct relation between joule and erg is:

physics energy and its forms introduction to work work introduction to work and energy

  1. $1\ J = 10^{-5} erg$

  2. $1\ J = 10^{5} erg$

  3. $1\ J = 10^{-7} erg$

  4. $1\ J = 10^{7} erg$

Show answer
Correct Option: D
Explanation:

Joule and erg both are units of work done. An erg is the amount of work done by applying a force of one dyne for a distance of one centimeter. In the CGS base units, it will be one gram centimeter-squared per second-squared. Whereas joule is the amount of work done by applying a force of one newton for a distance of one meter.

Thus,

$1 joule = 1 newton \times 1 m\\$

$1 joule = \dfrac{1 kg \times 1 m}{1 s ^{2}} \times 1 m\\$

$1 J = \dfrac{1000 g \times 100 cm}{1 s ^{2}} \times 100 cm \\$

$1 J = 10^{7} \ erg$

Thus option D is correct.

State the wrong statement 

physics energy and its forms introduction to work work introduction to work and energy

  1. Total work done by internal force in a system is always zero

  2. Work done is different as seen from different frames of reference

  3. In the absence of external forces and non-conservation force , the molecules energy of a system remains conserved

  4. a non conservation force always  do negative work

Show answer
Correct Option: D

A force $\vec {F} = -k(x\hat {i} + y\hat {j})$, where $k$ is positive constant, acts on a particle moving in the $x-y$ plane. Starting from the origin, the particle is taken along the positive x-axis to the point $(a, 0)$ and then parallel to the y-axis to the point $(a, a)$.

physics energy and its forms introduction to work work introduction to work and energy

  1. Work done by the force in moving particle along x-axis is $-\dfrac {1}{2}ka^{2}$

  2. Work done by the force in moving particle along x-axis is $-ka^{2}$

  3. Work done by the force in moving particle along y-axis is $-\dfrac {1}{2}ka^{2}$

  4. Total work done by the force for overall motion is $-ka^{2}$

Show answer
Correct Option: B,C

A man carries a load on his head through a distance of 5 m. The maximum amount of work is done when he

physics energy and its forms introduction to work work introduction to work and energy

  1. Movies it over an inclined plane

  2. Movies it over a horizontal surface

  3. Lift it vertically upwards

  4. All of the above

Show answer
Correct Option: C
Explanation:

The maximum work done by man will be when he lift it vertically upwards because in such situation the man has to exert force opposite to gravity that is in the direction of the displacement of load. 

A force of $5 N$ is applied on a $20 kg$ mass at rest. the work done in the third second is:-

physics energy and its forms introduction to work work introduction to work and energy

  1. $\dfrac{25}{8}J$

  2. $\dfrac{25}{4}J$

  3. $12 J$

  4. $25 J$

Show answer
Correct Option: A
Explanation:

Displacement in third second = displacement till 3rd second - Displacement till 2nd second 

=$\dfrac{a}{2}3^2-\dfrac{a}{2}2^2=\dfrac{5}{8}m$ (No term of ut because u=0)

Thus work done in third second =$5\times\dfrac{5}{8}=\dfrac{25}{8}J$