Physics

Forces, Energy and Machines

267 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 dynamics - explaining motion system of unit summary of si units system of units

$1$ Newton$=$ $K$ dyne, then what is the value of $K$?

  1. $1$
  2. $10^2$
  3. $10^5$
  4. $10$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Newton is in SI units that is Kg metre per second whereas Dyne is in Gram centimetre per second.

We know that $1 Kg = 1000 gm$ where as $1 metre = 100 cm$.
Hence to convert from SI units to CGS unit, we will have to multiply by a factor that is $1000\times100$.
$K=10^{5}$

Multiple choice maths percentages finding one number as percentage of another money and metric measures as percentage expressing one quantity as a percentage of another

A spider climbed $62\cfrac{1}{2}$% of the height of the pole in one hour and in the next hour it covered $12\cfrac{1}{2}$% of the remaining height. If pole's height is $192m$, then the distance climbed in second hour is:

  1. $3m$
  2. $5m$
  3. $7m$
  4. $9m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

First hour: 62.5% of 192m = 120m. Remaining height: 192 - 120 = 72m. Second hour: 12.5% of 72m = (1/8) * 72 = 9m.

Multiple choice physics a little effort, lot of work motion in application common machines introduction to simple machines

The law of a certain lifting machine is $P =W/50+ 1.5$. The velocity ratio of the machine is 100. Find the maximum possible mechanical advantage and maximum possible efficiency of the machine

  1. 50 and 50%

  2. 50 and 60%

  3. 60 and 60%

  4. 60 and 50%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The law of the machine is P = W/50 + 1.5. The maximum mechanical advantage is the reciprocal of the coefficient of W, which is 50. Efficiency is (Mechanical Advantage / Velocity Ratio) * 100, so (50/100) * 100 = 50%.

Multiple choice physics work and power commercial unit of energy power work and energy

A force of $ 2\hat { i } +3\hat { j } +2kN $ acts on a body for 4 s and produces a displacement of $3\hat {i} +4\hat {j} +5 \hat {k} m $ calculate the power ?

  1. 5 w

  2. 6 w

  3. 7 W

  4. 9 w
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given that,

Force  ,$F= 2 \hat i + 3\hat j + 2\hat k $  N
Displacement , $S= 3\hat i + 4\hat j +5 \hat k $ m 
Time Taken , $t= 4\ s$

Power, $P=\dfrac Pt = \dfrac{F\cdot S}{t}= \dfrac{6+12+10}{4}= \dfrac{28}4 = 7\ W$

Multiple choice chemistry materials around us and different types of houses materials around us matter and its states different states of matter
A solid cube of iron whose edge is 4 inches weighs 20.8 lbs. Determine the specific gravity of this sample of iron, if water weighs 62.4 pounds per cubic foot?
  1. $4.5$
  2. $5.2$
  3. $9.0$
  4. $27$
  5. $324$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$4$ inches $=$ $0.333$ foot


Since it is a solid cube, its volume is given by the formula $(side)^3$, that is, here its volume is $(0.333)^3$, that is $0.0369$ cubic foot.


Mass of the solid cube is $20.8$ pounds

Density $=$$\dfrac{Mass}{Volume}$

Thus, the density of the solid cube is $\dfrac{20.8}{0.0369}$, that is $563.68$ pounds per cubic foot.

Mass of water is $62.4$ pounds per cubic foot.

Thus, density of water is $\dfrac{Mass}{Volume}$, that is $\dfrac{62.4}{1}$, that is $62.4$ pounds per cubic foot.

Specific gravity of the solid iron  $= \dfrac {Density\ of\ solid\ iron} {Density\ of\ water}$

Thus, specific gravity of the iron is $=$ $\dfrac{563.68}{62.4}$, that is $9.033 \approx\ 9$

Hence, the correct option is C.

Multiple choice physics magnetic fields and electromagnetism magnetic flux density magnetic flux electromagnetic induction

Light with an energy flux of $18 w/cm^2$ falls on a non-reflecting surface at normal incidence. If the surface has an area of $20 cm^2$. Find the average force exerted on the surface during a 30 minute time

  1. $1.2 \times 10 ^ { - 6 } N$
  2. $2 .4\times 10 ^ { - 6 } N$
  3. $2.16 \times 10 ^ { - 3 } \mathrm { N }$
  4. $1.5\times 10 ^ { - 6 } N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The total energy falling on the surface is $U = \left( {18W/c{m^2}} \right) \times \left( {20c{m^2}} \right) \times \left( {30 \times 60} \right) = 6.48 \times {10^5}J$

therefore$,$ the total momentum delivered is 
$P = \dfrac{U}{c} = \dfrac{{\left( {6.48 \times {{10}^5}J} \right)}}{{\left( {3 \times {{10}^8}\,m/s} \right)}} = 2.16 \times {10^{ - 3}}\,kgm/s$
The average force exerted on the surface is 
$F = \dfrac{p}{t} =  = \dfrac{{2.16 \times {{10}^{ - 3}}}}{{0.18 \times {{10}^4}}} = 1.2 \times {10^{ - 6}}N$
Hence,
option $(A)$ is correct answer.

Multiple choice physics force and newton's laws of motion inertia and mass concept of inertia galileo's law and inertia

A tennis ball and a cricket ball, both are stationary. To start motion in them

  1. a less force is required for the cricket ball than for the tennis ball

  2. a less force is required for the tennis ball than for the cricket ball

  3. same force is required for both the balls

  4. nothing can be said
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Newton's laws of motion, an object with more mass requires more force to change the current state. Since, a cricket ball is heavier than a tennis ball, therefore, less force is required to start motion in tennis ball than in cricket ball.

Multiple choice standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

1 Newton $=$

  1. $10^4 dyne$
  2. $10^5 dyne$
  3. $10^6dyne$
  4. $10^7 dyne$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
S.I. unit of force is Newton and CGS unit of force is done.

We know $F=ma$
so, force can be expresses in S.I. Units as $Kg m s^{-2}$
and dyne can be expressed as $gcms^{-2}$
1 Newton= $kg ms^{-2}$ 
                 =$10^3 g*10^2 cms  s^{-2}$
                 =$10^5 g cm s^{-2}$
                 =$10^5 dyne$
Multiple choice electrostatic and magnetic analogy magnetism and matter magnetic effects of current and magnetism physics

Force between two identical bar magnets whose centres are  $r meters $ apart is $4.8 N,$ when their axis are in the same line. If the separation is increased to $2r$ meters, the force between them is reduced to:

  1. 2.4 N

  2. 1.2 N

  3. 0.6 N

  4. 0.3 N
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$F=\dfrac{\mu _{0}m _{1}m _{2}}{4\pi d^{2}}$
$F\propto \dfrac{1}{d^{2}}$
$Fd^{2}=Constant$
$F _{1}d _{1}^{2}=F _{2}d _{2}^{2}$
$4.8\times r^2=F _{2}(2r)^2$
$F _{2}=1.2  N$

Multiple choice physics motion and measurement of distances motion around us motion and rest moving things around us

Estimate the force exerted by a $75 \ W$ bulb on your finger tip (are $1\ cm^{2}$), when is at a distance of $8 \ cm$ from the bulb. (Assume $100\%$ absorption)

  1. $1 \ N$
  2. $3.1 \times 10^{-10} N$
  3. $4 \times 10^{-6} N$
  4. $2 \times 10^{-4} N$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} P=\frac { { \overline { S }  } }{ c } =\frac { { \frac { P }{ { 4\pi { d^{ 2 } } } }  } }{ c } =\frac { { \frac { { 75W } }{ { 4\pi { { \left( { 8.0\times { { 10 }^{ -2 } }m } \right)  }^{ 2 } } } }  } }{ { 3.00\times { { 10 }^{ 8 } }\, m/s } } =3.1\times { 10^{ -6 } }N/{ m^{ 2 } }. \ The\, \, force\, \, is\, \, pressure\, \, times\, \, area, \ we\, \, approximate\, \, the\, \, area\, \, of\, \, a\, \, fingertip\, \, to\, \, be\, \, 1.0\, c{ m^{ 2 } } \ F=PA=\left( { 3.1\times { { 10 }^{ -6 } }N/{ m^{ 2 } } } \right) \left( { 1.0\times { { 10 }^{ -4 } }{ m^{ 2 } } } \right) =3.1\times { 10^{ -10 } }N \end{array}$

Hence,
option $(B)$ is correct answer.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

A frictionless sloping plank 6m long. An oil drum of 300 N is raised up the sloping plank by an effort of 15 N. Calculate height to which oil drum rises is _____

  1. $2m$
  2. $7m$
  3. $3m$
  4. $0.3m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using the principle of conservation of energy or work input equals work output, Effort * distance moved by effort = Load * height raised. Here, 15 N * 6 m = 300 N * h, which gives h = 90 / 300 = 0.3 m.

Multiple choice maths percent and percentage use of percentages converting between fractions or decimals and percentages percentage of a quantity

Choose the correct answer from the alternatives given :
A spider climbed $62\frac{1}{2}%$ of the height of the pole in one hour and in the next hour it covered $12\frac{1}{2}%$ of the remaining height. If poles height is 192 m. then distance climbed in second hour is

  1. $3$ m
  2. $5$ m
  3. $7$ m
  4. $9$ m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Remaining height = $\left (192 - \dfrac{125}{2}\% of 192 \right ) = $192- 120$ = 72 m$
Required distance (distance covered in second hour) then,
$\dfrac{25}{2}\% of\ 72 $= $\dfrac{25 \times 72}{2 \times 100} = 9 m$

Multiple choice power work and power work, energy and power physics energy and its forms

The average power required to lift a $100kg$ mass through a height of $50$ metres in approximately $50$ seconds would be ( in J/s)

  1. $50$
  2. $5000$
  3. $100$
  4. $980$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$Power= Work/Time= F.s/t=mgs/t=(100\times 9.8\times 50)/50= 980W $


Hence correct answer is option $D $