Tag: physics

Questions Related to physics

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 %

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Correct Option: A
Explanation:

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

It is easier to draw up a wooden block along an inclined plane than to haul it vertically, principally because:

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

  1. the friction is reduced

  2. the mass becomes smaller

  3. only a part of the weight has to be overcome

  4. $g$ becomes smaller

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Correct Option: C
Explanation:

The vertical plane $W=mgh$
for inclined plane $W'=mghsin(Q)$
$sinQ<1$
$W>W'$
hence only one part of weight is to overcome

A pump ejects $12000\ kg$ of water at the speed of $4\ { m }/{ s }$ in $40\ second.$ Find the average rate at which the pump is working

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

  1. $2.4kw$

  2. $2.5kw$

  3. $2.3kw$

  4. $1.7kw$

Show answer
Correct Option: A
Explanation:
$F=ma=12000\times \dfrac {4}{40}=1200\ N$
$A=F/m=1200/1200=1/10\ m/s^2$
$s=ut +\dfrac {1}{2}at^2=0+\dfrac {1}{2}\times \dfrac {1}{10}\times 40\times 40=80\ m$
then, $W=Fs=80\times 1200=96000\ J$
rate of working, $P=\dfrac {W}{t}$
$P=\dfrac {96000}{40}=2400W=2.4\ kW$

The mechanical advantage of inclined plane of angle of inclination $60^{\circ}$ is equal to :

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

  1. $\dfrac{2}{\sqrt{3}}$

  2. $cosec 30^o$

  3. both (1) and (2)

  4. none of the above

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Correct Option: A
Explanation:

Mechanical advantage of an inclined plane at an angle $\theta$ is  $ \dfrac{Length }{height}$$ = \dfrac{l}{h} = \dfrac{1}{sin \theta}$


$ = cosec \theta = cosec 60^o = \dfrac{1}{sin 60^o} = \dfrac{2}{\sqrt{3}}$

Mechanical advantage is equal to 

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

  1. $2 \pi R \times 2 \pi r$

  2. $ 2 \pi R - 2 \pi r$

  3. $\displaystyle \frac{2\pi R}{2 \pi r}$

  4. None of these

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Correct Option: C

Akhil has to lift a load of 800 N onto a platform of 2 m height. Instead, he pushes the load up a ramp 4 m long. Find the force required to roll the load up the ramp.

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  1. 200 N

  2. 600 N

  3. 400 N

  4. 800 N

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Correct Option: C
Explanation:

Force required to roll the load up the ramp (F) $=\displaystyle \frac{load \times height}{distance}$
$= 800 \displaystyle \times \frac{2}{4} = 400 N$

The ratio of the radius of two wheels A and B are in the ratio 3 : 7 respectively and the ratio of their respective axles is 5 : 4. Identify the wheel and axle that has greater mechanical advantage?

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

  1. A

  2. B

  3. Both have same

  4. Can't say

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Correct Option: B
Explanation:

The mechanical advantage of a wheel and axle $= \displaystyle \frac{Radius \ of \ wheel}{Radius \ of \ the \ axle}$
$MA _A = \displaystyle \frac{R _1}{r _1} $ and  $MA _B = \displaystyle \frac{R _2}{r _2}$
Given $ r _1  :  r _2  = 5 : 4$
$R _1  :  R _2  = 3  :  7$
$ \displaystyle \frac{MA _A}{MA _B} = \frac{R _1}{r _1} \times \frac{r _2}{R _2}$
$\displaystyle = \frac{3}{5} \times \frac{4}{7} = \frac{12}{35}$
$MA _B >  MA _A$

In a wheel-axle arrangement, the radius of wheel is 25 times more than the radius of an axle. Find the mechanical advantage of the machine.

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

  1. 20

  2. 25

  3. 30

  4. 35

Show answer
Correct Option: B
Explanation:

The mechanical advantage of a wheel and axle $= \displaystyle \frac{Radius  of  wheel}{Radius  of  the  axle}$
Given radius of wheel $=$ 25 $\times$ radius of axle
$MA = \displaystyle \frac{25 \times radius  of  axle}{radius  of  axle} = 25$

Which of the following statements in NOT correct?

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

  1. In a first order lever, the fulcrum is placed between the effort and the load.

  2. The mechanical advantage of a second class levers is greater than 1 as load is situated in between to effort and fulcrum.

  3. An inclined plane in a hospital, helps in pushing a wheel chair easily.

  4. A crow bar is an example of second class level.

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Correct Option: A,B,C

An effort of 20 kgf is applied on a machine through a distance of 80 cm, when a load of 30 kgf moves through a distance of 1 cm. Calculate the velocity ratio of the machine.

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

  1. 40

  2. 80

  3. 160

  4. 60

Show answer
Correct Option: B
Explanation:

Velocity ratio $= \displaystyle \frac{distance \ of \ the \ effort}{distance \ moved \ by \ the \ load}$
$= \displaystyle \frac{80  cm}{1  cm}= 80$