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 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, $F _1 = 3N; F _2 = 5N; F _3 = 6N$

$F _1 + F _2 > F _3$

$F _2 + F _3 > F _1$

$F _3 + F _1  > F _2$


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

In a game of tug of war, three girls of team $A$ pull the rope with forces of $100 N$, $120 N$ and $170 N$. In team $B$, the three members pull the rope with forces of $130 N$, $150 N$ and $155 N$. Who will win the tug of war? What is the resultant force?

  1. Team $A$, $55 N$
  2. Team $B$, $55 N$
  3. Team $A$, $45 N$
  4. Team $B$, $45 N$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Resultant force is nothing but the total force acting on a body including their directions. If the object is at rest or it moves with a same velocity, the resultant force should be zero. All forces are acting on same direction, resultant force should be the sum of all the forces.

In this case, the forces applied by team A are 100 N, 120 N and 170 N. The total force is 100 N+120 N+170 N = 390 N. The forces applied by tema B are 130 N, 150 N and 155 N. The total force is 130 N+150 N+155 N=435 N.
Now, both the total forces are in the opposite direction as the team are in the opposite direction. So, the resultant force is 435 - 390 = 45 N. 
Therefore, Team B will win in the game as they apply more force of 45 N.

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

A force F is given by $F=at+bt^2$, where t is time. The dimensions of a and b are:

  1. $[MLT^{-3}]$and$ [MLT^{-4}]$
  2. $[MLT^{-4}]$and$ [MLT^{-3}]$
  3. $[MLT^{-1}]$and$ [MLT^{-2}]$
  4. $[MLT^{-2}]$and$ [MLT^{0}]$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given that $F=at+bt^2$ where $t$ is time.


For this equation to be dimensionally correct, the each term in the right hand side should have the dimensions of $F$

Dimensional formula of $F=[ MLT^{-2}]$

$\implies aT=[ MLT^{-2}]$
$\implies$ Dimension of $a$ is $[ MLT^{-3}]$

and
$\implies bT^2=[ MLT^{-2}]$
$\implies$ Dimension of $b$ is $[ MLT^{-4}]$

Hence, option $(A)$ is correct.

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

What happens when two forces are applied in the opposite direction on an object?

  1. Net force is the addition of forces.

  2. Net force is the subtraction of forces.

  3. Net force is the division of forces.

  4. Net force is the multiplication of forces.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When two forces are applied in the opposition direction on an object, the net force will be the difference between the two forces.

Multiple choice maths concept of directed numbers and number line subtraction of directed numbers subtraction of integers subtraction of integers on number line

A driver is $20$ m below sea level. If he goes further down by $10$m, then find his new position.

  1. $10$m
  2. $-10$m
  3. $30$m
  4. $-30$m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sea Level $\rightarrow$ $0$m

Original Position $\rightarrow$ $-20$m (Since he is below sea level)
New Position $\rightarrow$ $-$ ($20+10$) $\rightarrow$ $-30$m


Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Read the following statements carefully and pick out the correct choice of answer.
A: Electromotive force is expressed in Newtons.
B: Electric intensity is expressed in ${ VC }^{ -1 }$.

  1. Both A and B are correct.

  2. Both A and B are wrong.

  3. A is correct but B is wrong.

  4. A is wrong but B is correct.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Electromotive force is the voltage developed by any source of electrical energy such as a battery or dynamo. It is generally defined as the electrical potential for a source in a circuit.

It is not a force but voltage and its unit is volt.

Electric intensity at a point is defined as the force experienced per unit positive charge at a point placed in the electric field. 
Its unit is $Newton/Coloumb=NC^{-1}$

Both statements are wrong.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A person of mass $m$ is standing on one end of a plank of mass $M$ and length $L$ and floating in water. The person moves from one end to another and stops. The displacement of the plank is :

  1. $\dfrac {Lm}{(m+M)}$
  2. $Lm(M+m)$
  3. $\dfrac {(m+M)}{Lm}$
  4. $\dfrac {LM}{(m+M)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since there is no external horizontal force, the center of mass of the system remains stationary. m*x + M*X = 0, where x and X are displacements. The person moves distance L relative to the plank, so x_person = L - X_plank. Solving m(L - X) + MX = 0 gives X = -mL / (m+M). The magnitude is mL / (m+M).