Tag: introduction to simple machines

Questions Related to introduction to simple machines

In a lifting machine, the efforts required for lifting loads of $20$ N and $30$ N were $5$ N and $6$ N respectively. If the velocity ratio of the machine is $20$, determine efficiencies corresponding to loads of $20 $ N and $30$ N

physics simple machine common machines terms related to machines introduction to simple machines

  1. 25 % and 20%

  2. 35% and 55%

  3. 30% and 50%

  4. 60% and 65%

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Correct Option: A
Explanation:

Let us take first case,


 in which $load=20N , effort =5N ,VR=20$

$Efficiency=\dfrac{load}{VR*effort}*100$

Putting above values, we get

$Efficiency=\dfrac{20}{20*5}*100=20%$

In second case we have.  $load=30N , efoort =6N ,VR=20$

$Efficiency=\dfrac{load}{VR*effort}*100$

Putting values we get,

$Efficiency=\dfrac{30}{20*6}*100=25%$

Hence$ Efficiency=25%,20%$

The mechanical advantage for a pulley system is determined by

physics simple machine common machines terms related to machines introduction to simple machines

  1. counting the number of strands holding the resistance force.

  2. counting the number of strands holding and not holding the resistance force.

  3. adding the radii of the pulleys.

  4. multiplying the radii of the pulleys.

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Correct Option: B

If a machine overcomes a load $L$ and the distance travelled by the load is $L _d$. Similarly, the effort applied in the machine is $E$ and the distance travelled by effort is $E _d$, and $'T'$ is the time taken then velocity ratio can be written as 

physics simple machine common machines terms related to machines introduction to simple machines

  1. $\dfrac{E _d}{L _d}$

  2. $\dfrac{L _d}{E _d}$

  3. $\dfrac{E _d}{\sqrt{L _d}}$

  4. $\dfrac{\sqrt{L _d}}{E _d}$

Show answer
Correct Option: A
Explanation:

The VR is define as ratio of distance travelled by effort:distance travelled by load


$VR=\dfrac{{E}{} _{d}}{{L}{} _{d}}$

option A is correct.

In a lifting machine, an effort of 500 N is to be moved by a distance of 20 m to raise a load of 10,000 N by a distance of 0.8 m. Determine the velocity ratio and mechanical advantage.

physics simple machine common machines terms related to machines introduction to simple machines

  1. 25 and 20

  2. 23 and 22

  3. 20 and 30

  4. 25 and 35

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Correct Option: A
Explanation:
Distance moved by effort is 20m,that of load is 0.8m

$VR=\dfrac{{E}{} _{d}}{{L}{} _{d}}$

$VR=\dfrac{20}{0.8}$

$VR=25$

the load is 10,000N and effort=500N

$MA=\dfrac{{load}{} _{d}}{{effort}{} _{d}}$

$MA=\dfrac{10000}{500}$

$MA=20$

Fill in the blank.
In second order lever, velocity ratio 

physics simple machine common machines terms related to machines introduction to simple machines

  1. is greater than one

  2. is less than one

  3. it may be greater than one or less than one

  4. none of the above

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Correct Option: A
Explanation:

The VR of second order lever is always grater than 1 because effort arm is always longer than load arm.


$VR=\dfrac{{E}{} _{d}}{{L}{} _{d}},Vr>1$


In a lifting machine, an effort of 500 N is to be moved by a distance of 20 m to raise a load of 10,000 N by a distance of 0.8 m. Determine the effort lost in friction

physics simple machine common machines terms related to machines introduction to simple machines

  1. 100 N

  2. 120 N

  3. 80 N

  4. 0 N

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Correct Option: A

Efficiency of a machine can also be written as 

physics simple machine common machines terms related to machines introduction to simple machines

  1. $\dfrac{\text{velocity ratio}}{\text{mechanical advantage}} \times 100 $ %

  2. $\dfrac{\text{mechanical advantage}}{\text{velocity ratio}} \times 100 $ %

  3. $\dfrac{\text{mechanical advantage}}{\text{velocity of the gear}} \times 100 $ %

  4. None of the above

Show answer
Correct Option: B
Explanation:

$effiency=\eta=\dfrac{Machanical-advantage}{velocity-ratio}*100$

Fill in the blank.
In the first order of lever, velocity ratio is usually __than 1 but could be __ or equal to 1

physics simple machine common machines terms related to machines introduction to simple machines

  1. greater, less

  2. less, more

  3. greater, more

  4. less, less

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Correct Option: A

You do 1200 J of work with gears. If the gears do 1000 J of work, what is the efficiency of the gears?

physics simple machine common machines terms related to machines introduction to simple machines

  1. $93.33$ %

  2. $73.33$ %

  3. $83.33$ %

  4. $80.33$ %

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Correct Option: C
Explanation:

$\eta=\dfrac{Load}{effort}*100=\dfrac{1000}{1200}*100=83.33\%$

You do 1260 J of work with a wheel and axle. If the wheel and axle does 1200 J of work, what is the efficiency of the wheel and axle?

physics simple machine common machines terms related to machines introduction to simple machines

  1. More than 95 %

  2. Equal to 95 %

  3. Less than 95 %

  4. Less than 83.33 %

Show answer
Correct Option: A
Explanation:

$\eta=\dfrac{Load}{effort}*100=\dfrac{1200}{1260}*100=95.23\%$