Tag: physics

Questions Related to physics

A small ball bearing is releases at the top of a long vertical column of glycerine of height $2h$. The ball bearing falls through a height $h$ in a time $t _{1}$ and then the remaining height with the terminal velocity in time $t _{2}$ Let $W _{1}$ and $W _{2}$ be the work done against viscous drag over these height. therefore.

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

  1. $t _{1}< t _{2}$

  2. $t _{1}> t _{2}$

  3. $W _{1}=W _{2}$

  4. $W _{1}< W _{2}$

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Correct Option: A

No work is done by a force on an object if 

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

  1. the force is always perpendicular to its velocity

  2. the force is always perpendicular to its acceleration

  3. the object is stationary but the point of application of the force moves on the object

  4. the object moves in such a way that the point of application of the force remains fixed.

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Correct Option: A
Explanation:
The work done by a force F in displacing a particle through d is:
$W=\vec{F}\cdot \vec{d}=Fd\cos \theta$
If $\theta =90^o$
$W=Fd\cos 90^o=0$
Now direction of displacement is same as the direction of velocity.
So if force is always perpendicular to the velocity then no work is done.

A moving particle is acted upon by several forces $F _1, F _2, F _3 .....$ etc. One of the force is chosen, say $F _2$,  then which of the following statement about $F _2$ will be true.

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

  1. Work done by $F _2$ will be negative if speed of the particle decreases

  2. Work done by $F _2$ will be positive if speed of the particle increases

  3. Work done by $F _2$ will be equal to the work done by other forces if speed of the particle does not change

  4. If $F _2$ is a conservative force, then work done by all other forces will be equal to change in potential energy due to force $F _2$ when speed remains constant.

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Correct Option: A

The unit kg m$^2$s$^{-2}$ is associated with :

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

  1. work only

  2. kinetic energy only

  3. potential energy only

  4. all the above

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Correct Option: D
Explanation:

The given unit is that of Work and Energy.


Hence all the physical quantities mentioned have the same unit.

Option D is correct
−2

The unit N-s is equivalent to:

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

  1. J

  2. kgms$^{-1}$

  3. kgms$^{-2}$

  4. kgms

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Correct Option: B
Explanation:

unit of force in Newton($N$).

force =mass$\times$acceleration.
in units $N=kg.m.sec^{-2}$
so $N.s=kg.m.sec{-1}$
so best possible answer is option B.

Rahul took a wooden cube of volume $1000  {cm}^3$ and put it in water. He observed that $\displaystyle \frac{3}{5}th$ of its volume is below the level of water. Later, he floated the cube in a liquid of density $0.8  g  {cm}^{-3}$ and applied extra force on the cube to completely submerge it in the given liquid. Calculate how much extra force Rahul applied on the cube.

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

  1. 2 N

  2. 8 N

  3. 6 N

  4. 4 N

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Correct Option: A

1 J is equal to

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

  1. ${10}^{5}$ erg

  2. ${10}^{7}$ erg

  3. ${10}^{-7}$ erg

  4. none of these

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Correct Option: B
Explanation:

$1 J=1N\times1m$


$={10}^{5}dyne\times{10}^{2}cm$

$={10}^{7}erg $

The c.g.s. unit of work is

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

  1. N

  2. dyne

  3. erg

  4. J

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Correct Option: C
Explanation:

The $c.g.s.$ unit of work is $erg.$

The $m.k.s.$ unit of work is $N$

One erg is equal to

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

  1. $1 g cm s^{-2}$

  2. 1 Nm

  3. $10^7 J$

  4. $10^{-7}J$

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Correct Option: D

Select the correct statement for work, heat and change in internal energy

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

  1. Heat supplied and work done depends on initial and final states

  2. Change in internal energy depends on the initial and final states only

  3. Heat and work depend on the path between the two points

  4. All of these

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Correct Option: A