Physics

Forces, Energy and Machines

281 Questions

Forces, energy, and machines are fundamental physics concepts focusing on mechanics, work, power, and simple machines. These topics regularly appear in general science sections of competitive exams. Use these questions to practice calculating resultant forces, mechanical advantage, and work done in various scenarios.

Resultant force calculationsMechanical advantage of leversWork and power equationsApparent weight in elevatorsBending moments

Forces, Energy and Machines Questions

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

A barometer kept in a stationary elevator reads $76$ cm. If the elevator starts accelerating up the reading will be:

  1. Zero
  2. Equal to $76$cm
  3. More than $76$cm
  4. Less than $76$cm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The movement of elevator up will increase value of g which will result in increase in pressure leading to increase in reading of barometer.

Multiple choice physics pressure in liquids and gases common consequences of the atmospheric pressure atmospheric pressure and its consequences important points about atmospheric pressure

A barometer kept in a stationary elevator reads 76 cm. If the elevator starts accelerating up, the reading in barometer will be:

  1. Zero

  2. Equal to 76 cm

  3. More than 76 cm

  4. Less than 76 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since the elevator is accelerating up, so, the force will act in the downward direction.

Therefore, the reading in the barometer will be less than 76 cm

Multiple choice

The box is ___ heavy to lift.

  1. very

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

The weight prevents the box from being lifted. 'Too' is used to indicate an excessive degree that causes an inability to perform an action.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

The force between two bodies having charges $5C$ and $10C$ separated by distance of $0.5 m$ in air is :

  1. $18\times 10^{11}\ N$
  2. $9\times 10^{11}\ N$
  3. $9\times 10^{9}\ N$
  4. $18\times 10^{9}\ N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

By Coulomb's law, the force between two charges is $F=k \dfrac{q _1q _2}{r^2}=(9\times 10^9)\times \dfrac{5\times 10}{(0.5)^2}=18\times 10^{11} N$

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

There are two charges $+2\mu\ C\ and -3\mu\ C$. The ratio of forces acting on them will be 

  1. $2:3$
  2. $1:1$
  3. $3:2$
  4. $4:9$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There are two charges $+2\mu C$ and $-3\mu C$. The ratio of forces acting on them will be $F=\dfrac { { q } _{ 1 }{ q } _{ 2 }K }{ { r }^{ 2 } } $

$\dfrac { { F } _{ 1 } }{ { F } _{ 2 } } =\dfrac { { q } _{ 2 } }{ { q } _{ 1 } } =\dfrac { 3 }{ 2 } $ or  ${ F } _{ 1 }:{ F } _{ 2 }=3:2$

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

The apparent weight of a person of mass m in an elevator is 2mg. The elevator is moving

  1. up with an acceleration of $\frac{g}{2}$

  2. up with an acceleration of g

  3. up with an acceleration of 2g

  4. down with an acceleration of g
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The apparent weight is given by N = m(g + a) for upward acceleration. If N = 2mg, then m(g + a) = 2mg, which simplifies to g + a = 2g, so a = g. The elevator is moving upward with an acceleration of g.

Multiple choice physics oscillations a few applications of linear shm simple pendulum example of simple harmonic motion

A person weighing $60\ kg$ stands on a platform which oscillates up and down at a frequency of $2\ Hz$ and amplitude $5\ cm$. The maximum and minimum apparent weights are nearly: ($g$ = 10$\ m/s^2$)

  1. $108$ kg-wt, $12$ kg-wt
  2. $108$ kg-wt, $24$ kg-wt
  3. $54$ kg-wt, $12$ kg-wt
  4. $54$ kg-wt, $24$ kg-wt
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$a=\omega^{2}x$
So, $a _{max}=$ $\omega^{2}A$
We know that $\omega=2\pi  f$
So, $a _{max}=\dfrac{(2\pi\times 2)^{2}\times 5}{100}$
Case I:
$N-mg=ma _{max}$
$N=m(a _{max}+g)$
$=60(10+\dfrac{16\times \pi^{2}\times 5}{100})$
$=1080 $ 

$ N=108$ kg-wt

Case II:
$mg-N=ma _{max}$
or, $N=mg-ma _{max}$
$=60(10-8)$
$=120\ N=12$ kg-wt

Multiple choice physics simple harmonic motion a few applications of linear shm simple pendulum example of simple harmonic motion

A person normally weighing 60kg stands on a platform which oscillates up and down simple harmonically with a frequency $2Hz$ and an amplitude $5cm$.if a machine on the platform gives the person's weight,then consider the following statements :

  1. The maximum reading of machine will be $108$kg
  2. The maximum reading of machine will be $90kg$
  3. The minimum reading of machine will be $12kg$

  4. The minimum reading of the machine will be zero correct statements are:
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

Maximum a=$w^2A$
$=(4\pi)^2\times 0.05$
$=16 \pi^2\times 0.05$
$=8$
$mg=60 \Rightarrow m=\dfrac{60}{10}=6$
$W _{max}=m(g+a)$
$=6\times (18)$
$=108kg$
$W _{min}=6(g-a)
$=12kg

Multiple choice physics types of energy renewable and non-renewable resources renewable and non-renewable sources of energy substances, objects and energy

A body of mass $15\ kg$ is raised from certain depth. If the work done in raising it by $10m$ is $1620J$, its velocity at this position is$(g=10 { ms }^{ -2 })$:

  1. ${ 2\ ms }^{ -1 }$
  2. ${ 4\ ms }^{ -1 }$
  3. ${ 1\ ms }^{ -1 }$
  4. ${ 8\ ms }^{ -1 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

work done=PE+KE

$1620=mgh+\dfrac{mv^2}{2}$
$1620=15\times 10\times 10+\dfrac{15v^2}{2}=1500+\dfrac{15v^2}{2}$
$v=4m/s$

Multiple choice luminous intensity measurements physics

Light with energy flux 36$\mathrm { w } / \mathrm { cm } ^ { 2 }$ is incident on a well polished metal slate of side 2$\mathrm { cm }$ . Theforce experienced by it is

  1. 0.96$\mu N$
  2. 0.24$\mu N$
  3. 0.12$\mu N$
  4. 0.36$\mu N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The force exerted by light on a surface is F = P/c, where P is the power (energy flux * area). For a perfectly reflecting surface, F = 2IA/c. For an absorbing surface, F = IA/c. Assuming absorption, F = (36 W/cm^2 * 4 cm^2) / (3 * 10^8 m/s) = 144 / 3 * 10^-8 N = 4.8 * 10^-7 N = 0.48 uN. If reflected, it is 0.96 uN. Given the answer 0.96 uN, the metal plate is considered a perfect reflector.

Multiple choice physics energy transformations and energy transfers forms of energy and energy conservation energy for everything forms of energy

 person trying to lose weight by burning fat lifts a mass of $10kg$ upto a height of $0.5\, m\, with\, in\, 1000$ times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up? Fat supplies $3.8 \times 10^7 J$ of energy per kg which is converted to mechanical energy with a $20 \%$ efficiency rate. 

  1. $6.45 \times {10^{ - 3}}kg$
  2. $9.89 \times {10^{ - 3}}kg$
  3. $12.89 \times {10^{ - 3}}kg$
  4. $2.45 \times {10^{ - 3}}kg$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Work done per lift = mgh = 10 * 9.8 * 0.5 = 49 J. Total work for 1000 lifts = 49,000 J. With 20% efficiency, energy required from fat = 49,000 / 0.20 = 245,000 J. Fat energy density = 3.8 * 10^7 J/kg. Mass of fat = 245,000 / (3.8 * 10^7) = 6.447 * 10^-3 kg.

Multiple choice physics along with motion what forces can do? force and it's unit force and its effects

Study the impact force when a golfer drives a golf ball $230$ meters down the fairway.

  1. The impact force on the golf ball is greatest

  2. The impact force on the club head is greatest

  3. The impact force is the same for both

  4. The impact force has no effect on the club

  5. The impact force has no effect on the ball
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The impact force or impulse is given by $I=F\times t$  

 by Newton's third law both will exert an equal and opposite force on each other and time of impact is also same therefore  impact force (impulse) is same for both.

Multiple choice physics along with motion what forces can do? force and it's unit force and its effects

 A force of $15 N$ increases the length ofa by $1 \mathrm { mm }$. The additional force require increase the length by $2.5 \mathrm { mm }$ in N is 

  1. $2.25$
  2. $22.5$
  3. $37.5$
  4. $3.75$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

We know,

$Y=\dfrac{FL}{A\Delta L}$

For a wire, A,L,Y are constant.

$\dfrac{F}{\Delta L}=$constant

Let extra Force needed be $ F$,

$\dfrac{15}{1}=\dfrac{F+15}{2.5}$

$F+15=2.5\times 15$

$F=1.5\times 15=22.5$

Option $\textbf B$ is the correct answer