Tag: machines

Questions Related to machines

State true or false.
A simple pulley reduces the effort required to lift a heavy load.

physics machines levers and pulleys pulley pulleys

  1. True

  2. False

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Correct Option: A

A block of mass M on a horizontal smooth surface is pulled by a load of mass  M / 2  by means of a rope  AB and string BC as shown in the figure .The length and mass of the rope AB are L and  M / 2 respectively .As the block is pulled from A = L to AB = 0 its acceleration changes from 

physics machines levers and pulleys pulley pulleys

  1. $\frac{3g}{4}$ to g

  2. $\frac{g}{4} to\frac {g}{2}$

  3. $\frac{g}{4} to {g}$

  4. $\frac{3g}{2}$ to 2g

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Correct Option: A

What is the ideal mechanical advantage of a single fixed pulley? Can it be used as a force multiplier?

physics machines levers and pulleys pulley pulleys

  1. $1.5$, yes

  2. $1.5$, No

  3. $1$, yes

  4. $1$, No

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Correct Option: D
Explanation:

A single fixed pulley has an ideal mechanical advantage of 1 since the effort force is equal to the load force.
No, it cannot be used as a force multiplier, instead, it is used to change the direction of force applied.

$1000$ N force is required to lift a hook and $10000$ N force is requires to lift a load slowly. Find power required to lift hook with load with speed $v = 0.5 m/sec$

physics machines levers and pulleys pulley pulleys

  1. $5kw$

  2. $5.5kw$

  3. $1.5kw$

  4. $4.5kw$

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Correct Option: B
Explanation:

$P=F.V=(1000+1000)0.5$
$=\dfrac{11000}{2}=5500=5.5kw$

A pulley system has a velocity ratio $3$ and an efficiency of $80\%$. Calculate the effort required to raise a load of $300N$.

physics machines levers and pulleys pulley pulleys

  1. $125 N$

  2. $300 N$

  3. $150 N$

  4. $225 N$

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Correct Option: A
Explanation:
$Velocity\ Ratio = 3$

$Efficiency = 80/100$

$Mechanical \ Advantage = efficiency \times Velocity\  ratio$

$\Rightarrow \dfrac{80}{100} \times 3 $

$\Rightarrow 2.4$


$M.A = \dfrac{load}{effort}$

$2.4 = \dfrac{300 N}{Effort}$

$\Rightarrow Effort = \dfrac{300 N}{2.4} = 125N$

In a single fixed pulley, if the effort moves by a distance $x$ downwards, by what height is the load raised upwards?

physics machines levers and pulleys pulley pulleys

  1. $2x$

  2. $x$

  3. $x/2$

  4. $x/g$

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Correct Option: B
Explanation:

We know that for a single fixed pulley, Distance moved by effort is equal to the distance moved by load.
$ Distance\; moved \;by\; effort = x$
$\therefore Distance \;moved \;by \;load = x$

A pulley system has a velocity ratio $3$ and an efficiency of $80\%$. Calculate the mechanical advantage of the system.

physics machines levers and pulleys pulley pulleys

  1. $2.0$

  2. $3.0$

  3. $2.4$

  4. $1.4$

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Correct Option: C
Explanation:

$Velocity\ Ratio = 3$


$Efficiency = 80/100$

$Mechanical \ Advantage = efficiency \times Velocity\  ratio$

$\Rightarrow \dfrac{80}{100} \times 3 $

$\Rightarrow 2.4$

In a fixed pulley 

physics machines levers and pulleys pulley pulleys

  1. load and effort are equal

  2. load is greater than effort

  3. load is less than effort

  4. both have no relation

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Correct Option: A

A block and tackle system has the velocity ratio $3$. A man can exert a pull of $200kgf$. What is the maximum load he can raise with this pulley system if its efficiency is $60\%$

physics machines levers and pulleys pulley pulleys

  1. $250 kgf$

  2. $260 kgf$

  3. $350 kgf$

  4. $360 kgf$

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Correct Option: D
Explanation:

$Mechanical advantage = Velocity Ratio \times Efficiency $
$M.A = 3 \times \dfrac{60}{100} = 1.8$
$M.A = \dfrac{load}{effort} $
$\therefore load = M.A \times effort$
$\Rightarrow 1.8 \times 200 = 360kgf$

It is easy to draw water from a well when the rope passes over a pulley than drawing it directly. Because:

physics machines levers and pulleys pulley pulleys

  1. pulley adds more force

  2. pulley decreases the weight of the bucket

  3. pulley has a mechanical advantage of more than one

  4. pulley changes the direction of force

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Correct Option: D