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 general knowledge

It is easier to roll a stone up a sloping road than to lift it vertical upwards because

  1. work done in rolling is more than in lifting

  2. work done in lifting the stone is much more than rolling it

  3. work done in both is same but the rate of doing work is less in rolling

  4. work done in rolling a stone is less than in lifting it
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Rolling a stone up a slope requires less work than lifting it vertically because the force needed is much smaller when spread over a longer distance (mechanical advantage). When lifting vertically, you must overcome the full weight directly. Rolling spreads the work over more distance with less force. The other options incorrectly claim rolling requires more work or the same work.

Multiple choice general knowledge math & puzzles

A monkey, at the bottom of a well, begins climbing the wall. It climbs for one hour and rests the next hour. In one hour it climbs 4 meters. In the one hour it rests, it slips back 2 meters. If the height of the wall is 20 meters, then the time taken by the monkey to climb out of the well(in hours) is?

  1. 20

  2. 17

  3. 16

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

The monkey climbs 4m in one hour and slips 2m in the next, gaining 2m net every 2 hours. After 8 cycles (16 hours), it reaches 16m. In the next climb hour, it reaches 20m and climbs out before slipping back. So total time = 16 + 1 = 17 hours. The final climb hour doesn't need a subsequent rest hour since the monkey escapes.

Multiple choice general knowledge

Every 8 steps walked up reduces ----- calories?

  1. 6

  2. 8

  3. 10

  4. 15
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Walking upstairs is a high-intensity cardiovascular activity that burns more calories than level walking due to the work against gravity. The claim of 6 calories per 8 steps is a reasonable approximation for an average adult, though actual caloric expenditure varies based on body weight, speed, and fitness level.

Multiple choice general knowledge science & technology

It is easier to roll a stone up a sloping road than to lift it vertical upwards because

  1. work done in rolling is more than in lifting

  2. work done in lifting the stone is much more than rolling it

  3. work done in both is same but the rate of doing work is less in rolling

  4. work done in rolling a stone is less than in lifting it
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = force × distance. When rolling up a slope, the effective force needed is reduced (mg sinθ vs mg for vertical lift), so less work is done over the longer distance along the slope compared to lifting vertically.

Multiple choice softskills creativity

A mountain goat attempts to scale a cliff sixty feet high. Every minute, the goat bounds upward three feet but slips back two. How long does it take for the goat to reach the top?

  1. 36

  2. 60

  3. 58

  4. 40
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

To solve this problem, the user needs to know basic arithmetic and the concept of adding and subtracting. The goat bounds upward three feet but slips back two, so it gains one foot in altitude each minute. The user must keep track of the goat's progress until it reaches the top of the cliff, which is at an altitude of sixty feet.

Now, let's go through each option and explain why it is right or wrong:

A. 36: This option is incorrect because 36 minutes is not sufficient time for the goat to climb the sixty-foot cliff. In 36 minutes, the goat would have climbed 36 feet but slipped back 24 feet, for a net gain of only 12 feet.

B. 60: This option is incorrect because the goat does not climb sixty feet in sixty minutes. In sixty minutes, the goat would have climbed 60 feet but slipped back 40 feet, for a net gain of only 20 feet.

C. 58: This option is correct. In 58 minutes, the goat would have climbed 58 feet but slipped back 38 feet, for a net gain of 20 feet, which is enough to reach the top of the cliff.

D. 40: This option is incorrect because the goat does not climb forty feet in forty minutes. In forty minutes, the goat would have climbed 40 feet but slipped back 26.67 feet, for a net gain of only 13.33 feet.

Therefore, the Answer is: C. 58

Multiple choice

A monkey climbs 30 feet at the beginning of each hour and rests for a while when he slips back 20 feet before he again starts climbing in the beginning of the next hour. If he begins his ascent at 8.00 a.m., at what time will he first touch a flag at 120 feet from the ground?

  1. 4 p.m.

  2. 5 p.m.

  3. 6 p.m.

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

The monkey climbs 30 feet and slips back 20 feet each hour, gaining 10 feet net per hour. After 7 hours (from 8 a.m. to 3 p.m.), he reaches 70 feet. At the beginning of the 8th hour (starts at 3 p.m.), he climbs 30 feet from 70 to 100 feet. At the beginning of the 9th hour (starts at 4 p.m.), he climbs from 100 to 130 feet, touching the 120-foot flag at 6 p.m. (after 10 hours from 8 a.m., which is 6 p.m.).

Multiple choice

A man climbs up and a monkey climbs down a rope hanging from a tree with same uniform acceleration separately. If the respective masses of monkey and man are in the ratio 3 : 2, the common acceleration must be

  1. 7/g

  2. 5g

  3. g/9

  4. g/5

  5. g/11
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let T be the tension of a rope. When man climbs up with acceleration a, ... T - m1g = m1a …(1) When a monkey climbs down with same acceleration a ... m2g - T = m2a ….(2) Adding (i) and (ii), we get (m2 - m1)g = (m1 + m2)a Or (1 - m1 / m2)g = (m1 / m2 + 1)a Or (1 - 2 / 3)g = (2 / 3 + 1)a Or (1 / 3)g = (5 / 3)a Or, a = g / 5. Clearly, it is not equal to 5g, hence it is a wrong option.

Multiple choice

A monkey climbs 30 feet at the beginning of each hour and rests for a while when he slips back 20 feet before he again starts climbing in the beginning of the next hour. If he begins his ascent at 8.00 a.m. at what time will he touch a flag which is 120 feet from the ground?

  1. 4 p.m.

  2. 5 p.m.

  3. 6 p.m.

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

Net climb per hour = 30 - 20 = 10 ft. After 9 hours (8am to 5pm), monkey reaches 90 ft. At 5pm, starts at 90 ft, climbs 30 ft to reach 120 ft exactly. No slip back occurs because goal is reached during the climb.