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

A lift coming down is just about to reach the ground floor. Taking the ground floor as origin and positive direction upwards for all quantities, which of the following is correct ($x$=displacement, $v$= velocity, $a$=acceleration):

  1. $x < o, v<0, a>0$
  2. $x > 0, v < 0, a < 0$
  3. $x > 0, v < 0, a> 0$
  4. $x > 0, v >0,a >0$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If the lift is below the origin (ground floor), x < 0. If it is moving down, v < 0. If it is slowing down to reach the ground, it must have an upward acceleration, so a > 0.

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

Eqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force ?

  1. Eqbal

  2. Seema

  3. Both apply same force

  4. cant say
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Force of friction arises because of interlocking of irregularities on the two surfaces in contact. When a heavy object is placed on the floor, the interlocking of irregularities on the surface of box and floor become strong. This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus to push the heavier box, Seema has to apply a greater force than Eqbal.

Multiple choice physics forces - vectors and moments concept of force and its unit force - push or pull forces

Which of the following pairs of forces cannot be added to give a resultant force of $4N$?

  1. $2 N$ and $8 N$
  2. $2 N$ and $2 N$
  3. $2 N$ and $6 N$
  4. $2 N$ and $4 N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Resultant force, 

$F=\sqrt{F _1^2+F _2^2+2F _1F _2cos\theta}$. . . . . . . . .(1)
Lets consider the option A,

$F _1=2N$
$F _2=8N$

For maximum resultant force, $cos\theta=1$
From equation (1),
$F _{max}=\sqrt{F _1^2+F _2^2+2F _1F _2}=\sqrt{(F _1+F _2)^2}$
$F _{max}=F _1+F _2$
$F _{max}=8+2=10N$
For minimum resultant force, $cos\theta=-1$
$F _{min}=\sqrt{F _1^2+F _2^2-2F1F _2}=\sqrt{(F _1-F _2)^2}$
$F _{min}=\sqrt{(2-8)^2}=6N$
So, the $4N$ does not lie within this range. Thus it is not possible to have it as resultant force.
The correct option is A.

Multiple choice physics forces - vectors and moments concept of force and its unit force - push or pull forces

Two forces 12 N and 5 N are acting perpendicular to each other. Then the net force acting is.

  1. 17 N

  2. 18 N

  3. 7 N

  4. zero

  5. 13 N
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

$ \vec F _{net} = \vec F _1 +\vec F _2$

$| \vec F _{net}| = \sqrt{F _1^2 +F _2^2 +2F _1F _2\cos\theta}$
$| \vec F _{net}| = \sqrt{12^2 +5^2 +2\times 12 \times 5\cos 90^0}$
$| \vec F _{net}| = \sqrt{12^2 +5^2 }$
$| \vec F _{net}| = 13N$
Therefore, E is correct option.

Multiple choice physics forces - vectors and moments concept of force and its unit force - push or pull forces

Two forces of $12 \mathrm { N } \text { and } 8 \mathrm { N }$ acts upon a body. The resultant force on the body has maximum value of

  1. $4 \mathrm { N }$
  2. $0 \mathrm { N }$
  3. $20 \mathrm { N }$
  4. $8 \mathrm { N }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given,

$|\vec F _1|=12N$
$|\vec F _2|=8N$

The resultant force on the body is 
$|\vec R|=\sqrt{F _1^2+F _2^2+2F _1F _2cos\theta}$

For maximum value, $cos\theta=1$
$|\vec R|=\sqrt{(12)^2+(8)^2+2\times 12\times 8\times 1}$

$|\vec R _{max}|=\sqrt{144+64+24\times 8}$

$|\vec R _{max}|=\sqrt{400}=20N$
The correct option is C.

Multiple choice physics force concept of force and its unit force - push or pull forces

Which of the following pairs of forces will never give resultant force of $2N$

  1. $2N$ and $2N$
  2. $1N$ and $1N$
  3. $1N$ and $3N$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Because if these two forces Act then it cancelled out because they have the same value. Either it acts in same or opposite direction 
Multiple choice physics force concept of force and its unit force - push or pull forces

Two forces P and Q can support the body of weight W, one by one, when the body is on the inclined plane of inclination $\theta$ with horizontal and P and Q are acting parallel to the length and base of the inclined plane respectively. Hence

  1. $P^{2} + Q^{2} = W^{2}$
  2. $P^{2} - Q^{2} = W^{2}$
  3. $\cfrac{1}{P^{2}} + \cfrac{1}{Q^{2}} = \cfrac{1}{W^{2}}$
  4. $\cfrac{1}{P^{2}} - \cfrac{1}{Q^{2}} = \cfrac{1}{W^{2}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics force concept of force and its unit force - push or pull forces

You want to lift a heavy box. The force of gravity pulls it downwards with a force of $500N$. Your father applies an upward force of $220 N$ from below. How much force will you have to apply to lift it upwards?

  1. $720 N$
  2. $280 N$
  3. $180 N$
  4. $380 N$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The force of the gravitational pull is 500 N and the additional force of 220 N is applied in the opposite direction.
So, to lift the box, the box has to apply an extra force of 500 N - 220 N = 280 N in order to lift the box against the gravitational pull.
Resultant force is nothing but the total force acting on a body including their directions. Here, the gravitational force acts opposite to the force applied by the father and the boy.
Hence, the boy has to apply a force of 280 N to lift the box.

Multiple choice physics force concept of force and its unit force - push or pull forces

What will be the net force acting on an object when two equal forces are applied on an object in opposite directions?

  1. Sum of the forces.

  2. Zero

  3. Equal to each of the applied forces.

  4. Difference of the forces.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The forces acting on the object in the opposite directions are equal. The net force will be the difference of the two equal forces. Since both the forces are equal, net force is zero.

Multiple choice physics force concept of force and its unit force - push or pull forces

On a body, a force of $5N$ is applied towards North and another force of $2N$ is applied towards South. Net force on the body is

  1. $3N$
  2. $7N$
  3. $5N$
  4. $2N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When forces are applied inn the opposite directions, the forces get subtracted.
So, net force on the body$=(5-2)N=3N$

Multiple choice physics force concept of force and its unit force - push or pull forces

To move a roller, a force of $300 N$ is required. You alone can produce a force of $30 N$. How many of your friends who are equally strong as you should join you to move the roller?

  1. 9

  2. 10

  3. 5

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Force applied by you $= 30 N =$ force applied by any of your friends.
So, let there be $x$ people in total to push the roller.
When $x$ people, each giving a force of $30N$, give force in same direction, total force = $30xN$
To move the roller, $30x=300$
So, $x=\frac{300}{30}=10$
$\therefore$ number of friends to join you $=(10-1)=9$

Multiple choice physics force concept of force and its unit force - push or pull forces

$2N$ force is applied on a body from the right side and $6$ N is applied from the left side .The resultant force will be __________ N

  1. $8$
  2. $4$
  3. $3$

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If two forces act in the opposite directions on an object,the net force acting on it is the difference between the two forces.

Multiple choice physics force concept of force and its unit force - push or pull forces

If two forces act in opposite directions on an object,the net force acting on it is the

  1. Addition of two forces

  2. Difference of two forces

  3. Division of two forces

  4. Multiplication of two forces
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Forces applied on an object in the same direction add to one another.

If two forces axt in the opposite directions on an object,the net force acting on it is the difference between the two forces

Multiple choice physics force concept of force and its unit force - push or pull forces

Force acting on a particle is 5 N. If the unit of length and time are doubled and unit of mass is halved then the numerical value of the force in the new unit will be ________ times the initial value.

  1. 1

  2. 2

  3. 3

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

Force = $\displaystyle 5: : \frac{kg\times m}{sec^{2}}$
If unit of length and time are doubled and the unit of mass is halved
Then the unit of force will be $\displaystyle \left ( \frac{\frac{1}{2}\times 2}{(2)^{2}} \right )=\frac{1}{4}$ times
Hence the numerical value of the force will be 4 times (as numerical value $\displaystyle \propto\frac{1}{unit}$)

Multiple choice physics force concept of force and its unit force - push or pull forces

Which of the following sets of concurrent forces may be in equilibrium?

  1. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=1N$
  2. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=9N$
  3. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=6N$
  4. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=15N$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
"Forces are in equilibrium when vector sum of these three forces is zero and they form a triangle.
For a triangle, the sum of the two sides is always greater than the third side
Therefore, $F _1 = 3N; F _2 = 5N; F _3 = 6N$

$F _1 + F _2 > F _3$

$F _2 + F _3 > F _1$

$F _3 + F _1  > F _2$