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 rotational motion of a rigid body and moment of inertia motion of rigid body rigid body equilibrium of a rigid body

Calculate the force required to lift a load of $60\ N$, placed at a distance of $3\ m$, from the fulcrum if the effort force is applied at a distance of $6\ cm$ from the fulcrum.

  1. $300\ N$
  2. $3000\ N$
  3. $1500\ N$
  4. $30\ N$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In order to lift the load we have to apply force such that it can balance the torque by load.

Or, Total torque shold be zero.
We know  $\tau = r \times F$
$\Rightarrow \tau _{total} = (3)60 - (0.06)F$... where F is force required.
$\Rightarrow (3)60 = (0.06)F$

$\Rightarrow F = 3000N$
Therefore, B is correct option.

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 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

Two equal poles repel each other with a force of 10$^{-3}$ N. When placed 2cm apart in air, the pole strength of each is (in amp-m).

  1. 4$\pi $

  2. 2

  3. 4
  4. 2$\pi $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$F=10^{-3}N$
$d=2cm$
$m _{1}=m _{2}=m$
$F=\dfrac{\mu _{0}m _{1}m _{2}}{4\pi d^{2}}$

$10^{-3} = \dfrac{10^{-7}\times m^{2}}{(2\times 10^{-2})^2}$
$m=2Am$

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 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 $= $\dfrac{25 \times 72}{2 \times 100} = 9 m$