Tag: concept of force and its unit

Questions Related to concept of force and its unit

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. $0.48 s$

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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

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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.

State whether true or False 
10 mN is equal to $10^{-3}$ dynes.

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: B
Explanation:

Newton (N) is a SI unit of Force while dyne is a CGS unit of force.   


Relation between them is given as 


$1 dyne=1*10^{-3}*1*10^{-2}N$
$1 dyne =10^{-5}N$
$1 N = 10^5 dyne$
$10 \ mN = 10 \times 10^{-3} N= 10^{-2} N = 10^{-2} \times 10^{5} dyne$
$10 \ mN=10^{3}dyne$

Which of the following laws represents the qualitative measure of force?

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

  1. Newton's first law of motion

  2. Fleming's right hand rule

  3. Fleming's left hand rule

  4. Zeroth law of thermodynamics

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Correct Option: A
Explanation:

Newton's first law of motion represents the qualitative measure of force.It states that:

An object remains in the state of rest or of uniform motion in a straight line unless compelled to change that state by an applied unbalanced force.
All objects resist change in their state of motion. The tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia. This is why, the first law of motion is also known as the law of inertia.

The state of rest or state of motion of a body can be changed by using

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

  1. Pressure

  2. Force

  3. Heat

  4. None of these

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Correct Option: B
Explanation:

First law of motion:

A body in rest or a body in motion will continue to do that unless and until an external force is applied on it.
Force will accelerate or decelerate a body.
 

A force is a result of:

physics force and types of force concept of force and its unit force - push or pull forces

  1. interaction between two bodies

  2. interaction of one body with itself

  3. friction

  4. all of the above

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Correct Option: A
Explanation:

One object exerts a force on the other object due to their mutual interaction when the objects either are in contact with each other or placed at certain distance apart.