Tag: concept of force and its unit

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Multiple choice physics force and types of force introduction to force what is force? 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.

  1. $0.12 s$

  2. $0.24 s$

  3. $0.36 s$

  4. $0.48 s$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $10\ unit$

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

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

  4. $20\ unit$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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-

  1. 5.6

  2. 56

  3. 0.56

  4. 560
Reveal answer Fill a bubble to check yourself
B Correct answer
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$

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

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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


Relation between them is given as 


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

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

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

  1. Newton's first law of motion

  2. Fleming's right hand rule

  3. Fleming's left hand rule

  4. Zeroth law of thermodynamics
Reveal answer Fill a bubble to check yourself
A Correct answer
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.