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

At which height would potential energy be the greatest?

  1. 200 ft / 21 m

  2. 250 ft / 76 m

  3. 300 ft / 91 m

  4. 325 ft / 99 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Gravitational potential energy is calculated as PE = mgh. Since mass and gravity are constant, the potential energy is greatest at the highest point.

Multiple choice

What formula is used to calculate work?

  1. work = distance x area

  2. work = force x distance

  3. distance = work x force

  4. force = speed x distance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The scientific definition of work is the product of the force applied to an object and the distance the object moves in the direction of that force (W = F * d).

Multiple choice

How do you calculate slope?

  1. Rise/Run

  2. Run/Rise

  3. Rise + Run

  4. Rise x Run
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Slope is defined as the change in the vertical direction (rise) divided by the change in the horizontal direction (run).

Multiple choice

force x distance =

  1. work

  2. stress

  3. power

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

Work done is defined as the product of the force applied and the distance moved in the direction of the force.

Multiple choice

Complete the formula: Pressure = Force divided by

  1. Area

  2. Volume

  3. Length

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

Pressure is defined as the force applied perpendicular to the surface of an object per unit area. Therefore, the formula is Pressure = Force / Area.

Multiple choice physics measurements and units measuring mass measurement of mass measuring instruments

A child stands on a bathroom scale while riding in an elevator. The child's weight when the elevator is not moving is 100 Ibs. What does the scale read when the elevator accelerates upward while travelling downward?

  1. greater than 100 Ibs

  2. less than 100 Ibs

  3. exactly 100 Ibs

  4. The same as it reads when accelerating downward while travelling upward, by symmetry.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given,

When lift is not moving, gravity force act downward, weighing machine show $\vec{F}=m\vec{g}=100\,lbs\,$force.

When lift start moving upward with acceleration$\vec{a}$, Normal reaction force on child increase by $m\vec{a}$

Therefore, net weight on weighing machine become, $\vec{F}=m\vec{g}+m\vec{a}$

Hence, scale will show weigh greater than $100\,lbs$force.

Multiple choice physics measurements and units measuring mass measurement of mass measuring instruments

A body of mass $32 \,kg$ is suspended by a spring balance from the roof of a vertically operating lift and going downward from rest. At the instants the lift has covered $20 \,m$ and $50 \,m$, the spring balance showed $30 \,kg$ and $36 \,kg$ respectively. Then the velocity of the lift is:

  1. decreasing at $20 \,m$ and increasing at $50 \,m$
  2. increasing at $20 \,m$ and decreasing at $50 \,m$

  3. continuously decreasing at a steady rate throughout the journey

  4. constantly increasing at constant rate throughout the journey.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Fbd

We know that,

$N=m\left( g-a \right)$

So, if $N<mg$

It is a case of downward acceleration

Then, the velocity is increase

Again, if $N>mg$

It is a case of downward retardation

Then, the velocity is decreases

Hence, the velocity is increasing at $20$ m and decreasing at $50\ m$

Multiple choice physics measurements and units measuring mass measurement of mass measuring instruments

A boy whose mass is $50$ kg stands on spring balance inside a lift. The lift starts to ascend with an acceleration of $2{ m/s }^{ -2 }$. The reading of the machine or balance (g = 10${ m/s }^{ -2 }$) is

  1. 50 kg

  2. zero

  3. 49 kg

  4. 60 kg
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The apparent weight in an accelerating lift is W = m(g + a). Here, W = 50 * (10 + 2) = 50 * 12 = 600 N. Converting back to kg-force, the reading is 60 kg.

Multiple choice physics measurements and units measuring mass measurement of mass measuring instruments

A man is standing on a weighting machine with a block in his hand. The machine records $W$. When he takes the block upwards with some acceleration the machine records $W _1$. When he takes the block down with some acceleration, the machine records $W _2$. Then choose correct option 

  1. $W _1 = W = W _2$
  2. $W _1 < W < W _2$
  3. $W _2 < W < W _1$
  4. $W _2 = W _1 > W$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When the block is accelerated upward, the man exerts more force on the machine (W1 > W). When accelerated downward, the man exerts less force on the machine (W2 < W). Thus, W2 < W < W1.