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

What happens when the height of an inclined plane decreases?

  1. The mechanical advantage and effort both decrease.

  2. The mechanical advantage and effort both increase.

  3. The mechanical advantage increases, but effort decreases.

  4. The mechanical advantage decreases, but effort increases.

  5. It will not have any effect on the mechanical advantage.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The mechanical advantage of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. So, when the height of an inclined plane decreases, the mechanical advantage increases, but the effort decreases.

Multiple choice

A lighter child can move a heavier child on a seesaw if :

  1. he stands on it

  2. he moves closer towards the fulcrum

  3. moves away from the fulcrum

  4. he lies on it

  5. he can not do this
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Yes, because it is a type of class - I lever, in this type of lever if the effort arm is longer than the load arm than the lever acts as a force multiplier.

Multiple choice

Which of the following has the highest potential energy?

  1. 10 kg stone at a height at 20 m

  2. 50 kg stone at a height at 2 m

  3. 40 kg stone at a height of 5 m

  4. 30 kg stone at a height of 7 m

  5. 20 kg stone at a height of 8 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This has highest potential energy. P.E= mgh, where m=30 kg, h= 7 m, g=gravitational force, hence so P.E. = 30 * 7 = 210 joule

Multiple choice

If two weightlifters A and B lift a 100-pound barbell above their heads in 20 seconds and 10 seconds, respectively to same heigth which of the following statements is/are correct?

  1. Both lifters do the same amount of work.

  2. No work is done.

  3. Lifter A does twice the amount of work as that of B.

  4. Lifter A does half the amount of work as that of B.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Both lifters A and B do the same amount of work because they apply the same force to lift the same barbell above their heads and the displacement  is also same W = FS cos0 = FS 

F is force applied  , S is the  displacement in same direction

 

Multiple choice

Which of the following theorems states that if three forces acting at a point are in equilibrium then each of the force is directly proportional to the sine of the angle between the remaining two forces?

  1. Cauchy's theorem

  2. Pythagoras theorem

  3. Lami's theorem

  4. Leibnitz theorem
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Lami's theorem states that if three forces acting at a point are in equilibrium then each of the force is directly proportional to the sine of the angle between the remaining two forces.

Multiple choice

If the two forces applied to an object act in the same direction, then the resultant force acting on the object will be equal to which of the following?

  1. It will be equal to the difference between the two forces.

  2. It will be equal to the sum of the two forces.

  3. It will be equal to zero.

  4. It will be equal to the product of the two forces.

  5. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is the correct option. If the two forces applied to an object act in the same direction, then the resultant force acting on the object will be equal to the sum of the two forces.

Multiple choice

If the two forces applied to an object are equal in magnitude and act in opposite directions, then the net forces acting on the object ____________.

  1. will be zero

  2. will be equal to the sum of the two forces

  3. will be equal to the greater of the two forces

  4. will be equal to the product of the two forces

  5. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct option. If the two forces applied to an object are equal in magnitude and act in opposite directions, then the net forces acting on the object will be zero.

Multiple choice

Asha lifts a doll from the floor and places it on a table. If the weight of the doll is known, what else does one need to know in order to calculate the work done by Asha on the doll?

  1. Time taken

  2. Height of the table

  3. Mass of the ball

  4. Cost of the doll and table
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Work done is mgh. Here, we know the weight or mg, so we need to know the height of the table where the doll is placed in order to calculate work done.

Multiple choice

While running on a horizontal level road, a man holds an umbrella in the direction of the rain. If he stops, then in order to protect himself from the rain, he should hold it

  1. vertically as before

  2. inclined to the front

  3. inclined to the back

  4. at an angle of 45o

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When a person runs, they must tilt their umbrella forward to counter their horizontal velocity relative to the falling rain. When they stop, their horizontal velocity becomes zero, so the rain falls straight down relative to them, meaning they must hold the umbrella vertically as before they started moving.

Multiple choice

The forces directly proportional to the length of the nonpolar part of the substance is:

  1. London dispersion force

  2. Electrostatic force

  3. Nuclear forces

  4. Magnetic forces
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction. Van der Waals-London forces grow with the length of the nonpolar part of the substance.