Tag: common machines

Quizzes (4) Questions (140)

Questions Related to common machines

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

A nut can be opened by a lever of length $0.25$ m by applying a force of $80$ N. What should be the length of the lever if a force of $32$ N is enough to open the nut?

  1. <span>$625$ m</span>

  2. <span>$1625$ m</span>

  3. <span>$0.625$ m</span>

  4. <span>$6.25$ m</span>
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the principle of moments: F1 * L1 = F2 * L2. 80 N * 0.25 m = 32 N * L2. L2 = (80 * 0.25) / 32 = 20 / 32 = 0.625 m.

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

A rubber ball dropped from a height of $20\ m (g = 10\ m/s^{2})$ falls on the roof of an elevator going up at $2\ m/s$. If the collision of the ball with the elevator is elastic, the ball rebounds with a velocity of

  1. $20\ m/s$

  2. $22\ m/s$

  3. $24\ m/s$

  4. $26\ m/s$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Velocity of ball before impact: v = sqrt(2gh) = sqrt(2 * 10 * 20) = 20 m/s (downward). Elevator velocity = 2 m/s (upward). Relative velocity of ball w.r.t elevator = 20 - (-2) = 22 m/s. After elastic collision, it rebounds at 22 m/s relative to the elevator. Absolute velocity = 22 + 2 = 24 m/s.

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

A man of mass $80kg$ carrying a load of $20kg$ walks up a stair case in $20s$. If the number of steps is $40$ and width and height of each step are $20cm$ and $15cm$ respectively. The efficiency of the man is

  1. $20 \%$

  2. $25\%$

  3. $40\%$

  4. $50\%$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Total mass = 100 kg. Total height = 40 * 0.15 m = 6 m. Work done = mgh = 100 * 10 * 6 = 6000 J. Power output = 6000 / 20 = 300 W. Assuming human efficiency is related to power, this question is ambiguous without a defined input power.

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

A man uses a crowbar of length $1.5m$ to raise a load of $75kgf$ by putting a sharp edge below the bar at a distance $1m$ from his hand. Calculate the mechanical advantage. 

  1. $0$

  2. $1$

  3. $2$

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

Load $ = 75 kgf$
Length of crowbar $= 1.5 m$
Effort arm $= 1 m $
So, Load Arm $= \text{Length of crowbar - Effort arm}$


$\Rightarrow 1.5 - 1 = 0.5 m$
Mechanical Advantage $= \dfrac{\text{Effort Arm}}{\text{Load Arm}} = \dfrac{1}{0.5} =2$

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

A water -pump driven by petrol raises water at a rate $ 0.5 m^3/min $ from a depth of 30 m. if the pump is 70% efficient, what power is developed by the engine?

  1. 1750W

  2. 2450W

  3. 3500W

  4. 7000W
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work done per minute = mgh = (0.5 m^3 * 1000 kg/m^3) * 10 m/s^2 * 30 m = 150,000 J. Power output = 150,000 J / 60 s = 2500 W. Power input = Output / Efficiency = 2500 / 0.7 = 3571 W. 3500 W is the closest answer.

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

A $20\ N$ metal block is suspended by a spring balance. A beaker containing some water is placed on a weighing machine which reads $40\ N$. The spring balance is now lowered so that the block gets immersed in the water. The spring balance now reads $16\ N$. The reading of the weighing machine will be 

  1. $36\ N$

  2. $60\ N$

  3. $44\ N$

  4. $56\ N$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The block loses 20 - 16 = 4 N of weight in water, which is the buoyant force. By Newton's third law, the water exerts an equal and opposite upward force on the block, so the weighing machine reading increases by 4 N. New reading = 40 + 4 = 44 N.

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

A man uses a crowbar of length $1.5m$ to raise a load of $75kgf$ by putting a sharp edge below the bar at a distance $1m$ from his hand. Calculate the effort needed.

  1. $75kgf$

  2. $375kgf$

  3. $37.5 gf$

  4. $37.5kgf$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Load $ = 75 kgf$
Length of crowbar $= 1.5 m$
Effort arm $= 1 m $
So, Load Arm $= \text{Length of crowbar - Effort arm}$
$\Rightarrow 1.5 - 1 = 0.5 m$
Mechanical Advantage $= \dfrac{\text{Effort Arm}}{\text{Load Arm}} = \dfrac{1}{0.5} =2$


Effort needed $= \dfrac{\text{Load}}{\text{Mechanical Advantage}} = \dfrac{75}{2} = 37.5 kgf$

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

A boy can exert a maximum effort of $250\  N$, so he uses an inclined plane to lift the load up. What should be the minimum length of the plank used by him to lift a mass of $ 50 \ kg$ to a height of $1 \ m$ ?

  1. $2$ $ m $

  2. $5$ $&nbsp;m $

  3. $25$ $ m$

  4. $6$ $ m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Work done  $W = mgh$
$W = 50\times 10\times 1$  $N$
$W=500 N $
$W =$ Effort $\times$ distance
Distance$=500/250= 2m$