Tag: physics

Questions Related to physics

A force between two objects come into play when

physics force and types of force introduction to force what is force? concept of force and its unit

  1. Both objects are very heavy

  2. Both objects move with some speed

  3. Both objects interact with each other

  4. All

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Correct Option: C
Explanation:

At least two objects must interact for a force to come into action.

An interaction of one object with another object ,results in a force between the two objects.

Pulling of a cart/tram is an example of

physics force and types of force introduction to force what is force? concept of force and its unit

  1. Resultant force

  2. Gravitational force

  3. Contact force

  4. Action at a distance force

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Correct Option: C
Explanation:

The contact forces represent the result of physical contact between two objects,one by which force is exerted and the other on which force is exerted.

Suppose a man is standing behind a stationary car.Which of the following options will be correct?

physics force and types of force introduction to force what is force? concept of force and its unit

  1. The car will start moving towards the man

  2. The car will start moving away from the man

  3. The car will not move at all

  4. None

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Correct Option: C
Explanation:

Forces are due to an interaction.So the car will only move on application of force.

This S.I. unit of force is____

physics force and types of force introduction to force what is force? concept of force and its unit

  1. Joules

  2. Newton

  3. Watt

  4. Dyne

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Correct Option: B
Explanation:

F = ma

unit wise, $  \dfrac{kg m}{s^2} $
This is defined as Newton.
So, option B is correct.

A ball of mass $400 \ gm$ is dropped from a height of $5 \ m$. A boy on the ground hits the ball vertically upwards with a bat with an average force of $100 N$ so that it attains a vertical height of $20 \ m$. Find the time for which the ball remains in contact with the bat.

physics force and types of force introduction to force what is force? concept of force and its unit

  1. $0.12 s$

  2. $0.24 s$

  3. $0.36 s$

  4. $0.48 s$

Show answer
Correct Option: A
Explanation:

$M=0.4 gm$ $=0.4 kg$

${h _1} = 5\,m$ $,$ ${h _2} = 20\,m$
$g = 10 \,m/{s^2}$
Velocity of the ball after dropping $5m:u$
Velocity of the ball after being hit by the bat$:v$
${u^2} = 2g{h _1} ; u = \sqrt {\left( {2 \times 10 \times 5} \right)}  = 10\,m/s\,\left( {downwards} \right)$

${v^2} = 2g{h _2} ;  \left( {2 \times 10 \times 20} \right) = v = 20\,m/s\left( {upwards} \right)$

Change of momentum $=$impulse$=$ $m(v+u)=12\,kg\,m/s$
Force$=100N=12/t$
$t=$ time of contact $=0.12sec$
Hence,
option $(A)$ is correct answer.

Swimming is based on Newton's:

physics force and types of force introduction to force what is force? concept of force and its unit

  1. First law of motion

  2. second law of motion

  3. third law of motion

  4. law of gravitation

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Correct Option: C
Explanation:

When swimmer apply force on the water , then reaction force act on the man due to water. This force on the man drive man forward in the water.

This is an example of Newton’s 3rd law of motion.

If force $\vec {F} = 5\hat {i} + 3\hat {kj} + 4\hat {k}$ makes a displacement of $\vec {s} = 6\hat {i} - 5\hat {k}$, work done by the force is

physics force and types of force introduction to force what is force? concept of force and its unit

  1. $10\ unit$

  2. $122\sqrt {5}\ unit$

  3. $5\sqrt {122}\ unit$

  4. $20\ unit$

Show answer
Correct Option: A
Explanation:

We know that 

Work done $=force \times  displacement$
Work done $=\left( {5\widehat i + 6\widehat j + 4\widehat k} \right) \cdot\left( {6\widehat i + 0\widehat j - 5\widehat k} \right)$
Work done$=30-20=10$ $unit$
Hence,
option $(A)$ is correct answer.

If the interatomic spacing in a steel wire is ${ 2.8\times 10 }^{ -10 }$ m. and ${ Y } _{ steal }=2\times 10^{ 11 }N/m^{ 2 }$,then force constant in N/m is-

physics force and types of force introduction to force what is force? concept of force and its unit

  1. 5.6

  2. 56

  3. 0.56

  4. 560

Show answer
Correct Option: B
Explanation:

Interatomic  force  constant
$= Y \times inter\ atomic \ distance$
$ = 2\times 10^{11} \times 2.8\times 10^{-10}$
$ = 2\times2.8\times 10$
$ = 56 N/m$

State whether true or false:
The SI unit of force is newton.

physics force and types of force introduction to force what is force? concept of force and its unit

  1. True

  2. False

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Correct Option: A
Explanation:

The SI unit of force is the newton, symbol N. The base units relevant to force are: the metre, unit of length, symbol m, the kilogram, unit of mass, symbol kg, the second, unit of time, symbol s.

$ 1N = 1 \dfrac {kg m}{s^2} $
So, given statement is true.

If in a system of forces acting on a rigid body R.G  $\neq $ 0, then the given system of forces is equivalent to

physics force and types of force introduction to force what is force? concept of force and its unit

  1. degenerate wrench

  2. non-degenerate wrench

  3. a couple

  4. a single force

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Correct Option: B
Explanation:

Since neither force nor couple on body is zero, thus it is non-degenerate wrench.