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 lever common machines terms related to machines introduction to simple machines

A boy can exert a maximum force of $10$kg, i.e he cannot lift vertically a load of mass more than $10$kg. Now if he wants to raise a load of mass $20$kg on to a high eall, he can do it with the help of an inclined place making an angle $\theta$ with the horizontal. Find $\theta$.

  1. $60^o$
  2. $80^o$
  3. $30^o$
  4. $20^o$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$sin \theta=\dfrac{1}{M.A}=\dfrac{Effort}{Load}=\dfrac{10}{20}=\dfrac{1}{2}$
Thus, by placing a wooden plank at $\theta=30^o$ an angle equal to $30^o$ with the horizontal group can push the load of mass $20$Kg at any height by exerting a force(or effort) of $10$kg.

Multiple choice physics lever common machines terms related to machines introduction to simple machines

If a machine overcomes a load $L$ and the distance travelled by the load is $25 m$. Similarly, the effort applied in the machine is $E$ and the distance travelled by effort is $75 m$, and $'T'$ is the time taken,then velocity ratio is:

  1. $\dfrac{1}{3}$
  2. $\dfrac{2}{3}$
  3. $\dfrac{3}{1}$
  4. $1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The VR is define as ratio of distance travelled by effort:distance travelled by load

$VR=\dfrac{{E}{} _{d}}{{L}{} _{d}}$


$VR=\dfrac{25}{75}$

$VR=\dfrac{1}{3}$

option A is correct.
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

Buming of a meteorite in the Earth's atmosphere is an example of change of:

  1. heat energy into kinetic energy

  2. kinetic energy into heat energy

  3. kinetic energy into potential energy

  4. potential energy into heat energy
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

when meteorite falls its potential energy is converting into kinetic energy and when it enters earth atmosphere due to air friction its kinetic energy is reduced but potential energy is also decreasing as its height is decreasing , so we can conclude that its first potential energy converts to kinetic energy and then kinetic energy converts to heat energy.

so best possible answer is option B.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A person of weight 60 kg wants to loose 5 kg by going up and down 10m high stairs. Assume he burns twice as much fat while going up than going down. If 1 kg of fat is burnt on expending 7000 kcal. How many times must he go up and down to reduce his 7 kg weight? (Take $  g=10 \mathrm{ms}^{-2} )  $

  1. $ 1.8 \times 10^{3} $ times
  2. $ 2.4 \times 10^{3} $ times
  3. $ 1.7 \times 10^{3} $ times
  4. $ 2.1 \times 10^{3} $ times
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Energy used to go up $=mgh=60\times 10\times 10=6000\,J$

Energy used to come down $\dfrac{6000}{2}=3000\,J$

Energy used in one round trip $=9000\,J$

$1\,cal=4.5\,J$

$1\,J=\dfrac{1}{4.2\,cal}$

$9000\,J=\dfrac{9000}{4.2}=2142.85\,cal$

$7000\,kilo\,cal$ is required to burn $1\,kg$ mass

To reduce $5\,kg$ mass, energy required $=7000\times 5=35000\,kilo\,val$

Number of trip $=\dfrac{35000\times 1000}{2142.85}=1.7\times 10^{3}$
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A cyclist free-wheels from the top of a hill, gathers speed going down the hill, apply his brakes and eventually came to rest at the bottom of the hill. Which one of the following energy changes take place?

  1. Potential to kinetic to heat energy

  2. Kinetic to potential to heat energy

  3. Chemical to heat to potential energy

  4. Kinetic to heat to chemical energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Considering ground as zero potential
Initially $E = U + K = U + 0 = U$
Finally $E = U + K = 0 + 0 = 0$
So, initially it had some potential energy, it was converted to kinetic energy by gaining speed, it finally became zero so energy must have been lost as heat while applying brakes.

Multiple choice physics coulomb's law field strength and potential gradient electric field as gradient of potential relation between electric field and electric potential

Find the magnitude of the force on a charge of $12\mu C$ placed at point where the potential gradient has a magnitude of $6\times 10^{5}V\ m^{-1}$

  1. $5.20\ N$
  2. $7.20\ N$
  3. $6.20\ N$
  4. $8.20\ N$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Potential gradient is nothing but the rate of change of electric potential with position and it is equal to electric field at that point.


$\dfrac{dV}{dl}=E$=electric field

$\implies E=6\times 10^5Vm^{-1}$

Force on charge $=F=qE=12\times 10^{-6}\times 6\times 10^5$

$\implies F=7.2N$

Answer-(B)

Multiple choice evs - i rules are for everyone sustainability of natural resources adaptations - mangrove swamps, fast flowing rivers and treetops halophiles

What type of energy does wind possess ?

  1. Potential energy

  2. Kinetic energy

  3. Solar energy

  4. Heat energy
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electric power.

Multiple choice physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

A number of discs, each of momentum $M  kg  {m}/{s}$ are striking a wall at the rate of $n$ discs per minute. The force associated with these discs, in newtons, would be

  1. $\displaystyle\frac{Mn}{60}$
  2. $60 Mn$
  3. $\displaystyle\frac{M}{60n}$
  4. $\displaystyle\frac{n}{60M}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The force is $F=\dfrac{\Delta P}{dt}$

$momentum=M kg.m/s$
change in time=rate of dics striking wall 
$\Delta t=\dfrac{1}{n/minute}=\dfrac{60}{n}$ 
$F=\dfrac{\Delta P}{dt}=\dfrac{M}{60/n}=\dfrac{Mn}{60}N$

Multiple choice physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

A parachutist with total weight $75kg$ drops vertically onto a sandy ground with a speed of $2m{ s }^{ -1 }$ and comes to a halt over a distance of $0.25m$. The average force from the ground on her is close to

  1. $600N$
  2. $1200N$
  3. $1350N$
  4. $1950N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Initial velocity while dropping on the ground u=2m/s.
Parachutist was brought to rest within s=0.25 m
Therefore retardation f : $u^2=2fs; \; f=\frac{u^2}{2s}=8m/s^2$
Averarage force from ground on her close is F=mf=600 N