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 energy : forms and sources concept of energy energy for everything forms of energy

A man carries a heavy box on his head on a horizontal plane form one place to another. In this he does

  1. Maximum work

  2. No work

  3. Negative work

  4. Minimum work
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Work is defined as force multiplied by displacement in the direction of the force. When carrying a load horizontally, the force (gravity) acts vertically, while the displacement is horizontal. Since the angle between force and displacement is 90 degrees, the work done is zero.

Multiple choice physics trigonometrical ratios angles and sides naming the sides in a right angled triangle angle and their measurement

If the distance between a 13-foot ladder and a vertical wall is $5$ feet along the ground, how high can a person climb if the ladder is inclined against wall?

  1. $18$ feet
  2. $65$ feet
  3. $\cfrac{13}{5}$ feet
  4. $8$ feet
  5. $12$ feet
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Length of Ladder = 13 ft

Length between Ladder and Wall = 5 ft
by pythagoras theorum
(hypotenuse)^2 = (perpendicular)^2 + (base)^2
(13)^2 = (height of wall)^2+(5)^2
by solving
Height of Wall = 12 ft

Multiple choice physics mathematical methods multiplication of vectors products of vectors scalar product

Two forces of magnitude 20N and 20N act along the adjacent sides of the parallelogram and the magnitude of the resultant force of these two forces is $20\sqrt{3}$. Then the angle between these forces is:

  1. $30^0$
  2. $45^0$
  3. $90^0$
  4. $60^0$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The magnitude of the resultant of two vectors of equal magnitude P is R = 2P * cos(theta/2). Setting P = 20 and R = 20*sqrt(3) gives 20*sqrt(3) = 40 * cos(theta/2), so cos(theta/2) = sqrt(3)/2, leading to theta/2 = 30 degrees and theta = 60 degrees.

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

Which of the following actions can be grouped as push?

a. A cricket ball hit by a batsman.
b. A football player kicking the ball.
c. A girl is shutting the open door of a refrigerator. 

  1. Only a

  2. Only a and b

  3. only b and c

  4. a, b and c
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All the above examples can be grouped as push. As force is applied to move object away from the body.

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 dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Force $'F'$ exists between two point charges in air, if a medium having $\epsilon _{R} = 6$ is inserted between charges, the new force between them.

  1. Will increase by $6$ times
  2. Will decrease by $6$ times
  3. Will decrease by $\sqrt {6}$ times
  4. Will increase by $36$ times
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The force in a medium is F_medium = F_air / K. With K=6, the force decreases by 6 times.

Multiple choice physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

If the position of two like parallel forces shifted by one-fourth of the distance between the forces when the two forces are interchanged. The ratio of the two forces is:

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

Let forces be F1 and F2 at distance d. The resultant acts at x = F2*d / (F1+F2). If forces are swapped, new position x' = F1*d / (F1+F2). The shift is |x - x'| = d * |F1-F2| / (F1+F2) = d/4. Thus, 4|F1-F2| = F1+F2. If F1 > F2, 4F1 - 4F2 = F1 + F2 => 3F1 = 5F2 => F1/F2 = 5/3. If F2 > F1, 4F2 - 4F1 = F1 + F2 => 3F2 = 5F1 => F1/F2 = 3/5. Option D matches 3:5.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

The force acting on a 4gm mass in the energy region ${ U=8x }^{ 2 }$ at x= -2 cm is :

  1. 8 dyne

  2. 4 dyne

  3. 16 dyne

  4. 32 dyne
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given,

$m=4gm$
$U=8x^2$

The force acting on mass $m$ in the potential energy $U$  at $x=-2cm$ will be

$F=-\dfrac{dU}{dx}$
$F=-\dfrac{d(8x^2)}{dx}$
$F=-16x$
$|F| _{x=-2cm}=-16\times(-2)=32dyne$
The correct option is D.



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 $76 \mathrm { cm } ,$ If the elevator starts accelerating up the reading willbe 

  1. Zero
  2. equal to 76$\mathrm { cm }$
  3. more than 76$\mathrm { cm }$
  4. less than 76$\mathrm { cm }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When an elevator accelerates upward, the effective acceleration due to gravity increases (g_eff = g + a). This increases the pressure exerted by the mercury column in the barometer, resulting in a higher reading compared to the stationary state.

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 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  ${ F } _{ 1 }:{ F } _{ 2 }=3:2$