SIMPLE MACHINES
IMPORTANT QUESTIONS OF PAST PAPERS:
1. Define lever, principle of lever and derive formula for M.A of lever. (2013, 2016)2. Draw the figure of Wheel and Axle and calculate its M.A. (2015)
3. Define the following inclined plane and pulley. (2013)
4. Define machine and write down the names of four simple machines. (2011, 2009)
5. What is inclined plane? Calculate its M.A. (2014, 2017, 2009)
6. The two bodies of different masses are attached with a string which passes over a friction less pulley such that the bodies are moving vertical derive the formula. (2017)
7. Write down the kinds of lever. (2016)
8. Define input and output. (2010, 2014)
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IMPORTANT SYMBOLS:
• Effort applied = P
• load = W
• height = h
• Pitch of the screw = h
• Efficiency = η
• mass = m
• weight = W
• length = L
• Distance moved by load = h
• Distance moved by effort = d
• Length of Tommy bar = r
• Pitch of the screw = h
• length of the handle of screw jack = r
• Mechanical Advantage ( M.A ) = 𝒘 / 𝒑
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IMPORTANT FORMULA’S:
For pulley
•Mechanical advantages = 𝒘eight / efforts
•Input = Effort × Effort Arm
•Out put = Load × Load Arm
•Efficiency = output / Input
•Input = Output
Tommy bar and screw jack
•M.A = 𝟐л 𝐫 / h
Inclined plane
•M.A = l / h
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Force = Effort Weight = Load
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Questions/ Answer
Q.1: Define Machine and write down the names of four simple machines. Also write down the various purpose of machine.Ans: MACHINE: A device which performs the work in convenient (useful) manner is called Machine.
NAMES OF SIMPLE MACHINES:•Lever
•Screw
•Wedge
•Inclined plane
•Screw jack
•Wheel and Axle
VARIOUS PURPOSE OF MACHINE:
• To lift the heavy load. (Screw jack)
• To change the direction of force. (pulley)
• To transfer energy from one point to another point. ( lever)
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Q.2: Define Effort, Load, Input, Output, Mechanical Advantage and Efficiency.
Ans: EFFORT:(P) The force directly applied on the machine is called Effort. It is denoted by “p”.
LOAD: (W) The weight lifted by machine is called Load. It is denoted by “W”.
INPUT: The work done on a machine is called Input.
Formula:
Input = Effort × Effort Arm
Input = P × d
Input = P × d
OUTPUT: The work done by a machine is called Output.
Formula:
Output = Load × Load Arm
Output = W × h
Output = W × h
MECHANICAL ADVANTAGE: The ratio of Load and Effort is called Mechanical advantage. It is denoted by M.A.
Unit: Since M.A is ratio between two forces, it has no unit. It is expressed in numbers.
Formula:
EFFICIENCY: The ratio of output and input is called Efficiency.
Formula:
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Q.3: Define lever; describe working of lever, the terms used in liver, and principle of Lever and Mechanical Advantage of lever.
Ans:LEVER: A simplest machine, a strong metallic bar, which can be rotate about a fixed point, is called Lever.
WORKING OF LEVER: By applying a force on one end a bar, weight can be lifted at the other end.
Fulcrum: A fixed point around which lever is rotated, is called Fulcrum.
Effort Arm: The perpendicular distance between Effort and Fulcrum is called Effort Arm.
Moment of Effort: The product of Effort and Effort Arm is called Moment of Effort.
Load Arm: The perpendicular distance between Weight and Fulcrum is called Load Arm.
Moment of Load: The product of Load and Load Arm is called Moment of Load.
PRINCIPLE OF WORKING: The moment of effort is always equal to moment of load.
Moment of Effort = Moment of Load
Effort × Effort Arm = Load × Load Arm
P × d = W × h
This equation is called principle of lever.MECHANICAL ADVANTAGES OF LEVER:
According to principle of lever:
P × d = W × h
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Q. 4: Write down the kinds of lever.
Ans:KINDS OF LEVER: There are three kinds of lever.
➤FIRST KIND OF LEVER: If fulcrum F is in between Effort E and Weight (load) W, is called first kind of lever.
Example:
• A pair of scissors
• See-saw
• A common balance
➤SECOND KIND OF LEVER: If Load W is in between fulcrum F and Effort F is called second kind of lever.
Example:
• A door
• A punching machine
• A nut cracker
➤THIRD KIND OF LEVER: If Effort P is in between fulcrum F and load W, is called third kind of lever.
Example:
• Human arm
• Upper and lower jaws in the mouth
• A pair of forceps
• A fire tongs
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Q.5: Define Screw Jack. Find its Mechanical advantage.
Ans:SCREW JACK: A Screw jack is a machine which is commonly used to lift heavy load.
MECHANICAL ADVANTAGE:
When the handle is turned through one complete revolution in a circle of radius r, the effort moves through a distance 2 л r and the load is raised through a height h in this case,
Input = effort × distance moved by effort
Input = p × 2 л r Tommy bar
Output = Load × distance moved by load
Output = W × h
Input = p × 2 л r Tommy bar
Output = Load × distance moved by load
Output = W × h
For an ideal Machine,
Input = Output
P × 2 л r = W× h
P × 2 л r = W× h
The pitch of the screw is very small as compare to Tommy bar so the M.A of screw jack is very large.
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Q.6: What is inclined plane? Calculate its Mechanical Advantage.
Ans:INCLINED PLANE: A surface whose one end is higher than the other end is called an Inclined plane.
MECHANICAL ADVANTAGES:
Consider a smooth plane surface AB with make an angle ϴ with the horizontal. A load “W” is placed on inclined plane. Now effort “P” is applying on it through a distance l and weight W is raised to height.
Input = work done by effort
Input = Effort × distance
Input = P × l
Similarly,
Input = Effort × distance
Input = P × l
Out put = work done in raising the ways
Out put = weight × height
Output = W × h
Out put = weight × height
Output = W × h
For a Smooth, friction less ideal inclined plane
Output = Input
W × h = P × l
W × h = P × l
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Q.7: Define pulley. Find the M.A of Fixed Pulley and Movable Pulley.
OR
The two bodies of different masses are attached with a string which passes over a friction less pulley such that the bodies are moving vertical derive the formula.Ans:PULLEY: A pulley is grooved wheel supported in a frame called block such that wheel can turn about an axle in the block. The pulley can be suspended from a fixed beam by means of a hook.
FIXED PULLEY: A pulley whose block is fixed to a strong beam or ceiling and cannot move up and down is called Fixed pulley.
MECHANICAL ADVANTAGE: The Load W is tied to one end of the rope and effort P is applied at the other end. If we neglect the weight of the rope and friction then,
Input = Output
P × OA = W × OB
P × OA = W × OB
FIXED PULLEY: A pulley whose block is not fixed to a beam or ceiling is called movable pulley.
MECHANICAL ADVANTAGE: The load or weight W to be lifted is hung from the hook of the block. At every point in the rope, the tension is equal to the applied effort P. As both ends of the rope are pulling the weight W upwards so the effort P acting on the weight in the upward direction will be 2P. If we neglect the weight of the rope and friction then,
W = 2P
W / P = 2
M.A = 2
The M.A advantage of pulley is 2. It means double load can be lifted with the help of a simple movable pulley as compare to effort.
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Q. 8: Draw the figure of Wheel and Axle and calculate its M.A.
Ans:WHEEL AND AXLE: A Wheel with larger radius “R” and another with smaller radius “r” are fixed on the same shaft are called Wheel and Axle.
MECHANICAL ADVANTAGE: The effort “P” is applied at the rim of the wheel of radius “R” while the load “W” is lifted by a string wound around the axle. For one complete rotation, the effort moves through a distance 2 л R while the load raised through a distance 2 л r
If friction is neglect,
Output = Input
W × 2 л r = P × 2 л R
W × 2 л r = P × 2 л R
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Prepared By: Sir Waseem
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