machines

Question 1

What are the functions of a machine?

Answer 1

1. Lifting heavy loads by applying less force ( force multiplier )
2. By changing point of application to a convenient point.
3. By changing the direction of effort to a convenient direction
4. For obtaining a greater movement of load by a smaller movement of effort ( speed multiplier )

Question 2

What is a machine

Answer 2

A machine is a simple device by which we can either overcome a large resistive force at some point by applying a small force or effort at a convenient point and in a desired direction or by which we can obtain a gain in speed

Question 3

What is a load

Answer 3

resistive force to be overcome

Question 4

What is effort

Answer 4

Force applied on the machine to overcome load

Question 5

What is M.A?

Answer 5

ratio of load to effort
m.a = L/ E

Question 6

G.R: A machine cannot be used as a force multiplier and a speed multiplier simultaneously

Answer 6

because force multiplier = L>E
speed multiplier = E>L

Question 7

What is velocity ratio?

Answer 7

Ratio of velocity of effort to velocity of load

V.R = VE / VL
V.R = dE / dL

Question 8

What is work input?

Answer 8

Work done on the machine by the effort

Question 9

What is work output?

Answer 9

work done by machine on the load

Question 10

What is efficiency

Answer 10

ratio of work output to work input

when represented as % =( woutput / winput) × 100

Question 11

Reasons for decrease in efficiency

Answer 11

due to friction and weight of moving parts of the machine M.A decreases hence efficiency decreases

Question 12

What is effort point?

Answer 12

Point at which energy is supplied to the machine by applying effort

Question 13

What is load point

Answer 13

point where energy is obtained by overcoming the load

Question 14

What is the principle of a machine

Answer 14

For an ideal machine, output energy = input energy

Question 15

G.R: No machine can have efficiency > 1

Answer 15

output energy can never be greater than input energy as it will violate principle of conservation of energy

Question 16

3 reasons for loss of energy in actual machines

Answer 16

1. Moving parts are not weightless. smooth or frictionless
2. String if any is not perfectly elastic
3. Diff parts of the machine are not perfectly rigid

Question 17

How is energy lost in a machine?

Answer 17

most prominent - overcoming friction b/w moving parts of a machine. Energy lost appears as heat energy due to which moving parts of the machine get heated

Question 18

Relationship b/w M.A , V.R and Efficiency:

Answer 18

μ = M.A / V.R
M.A = V.R x μ

Question 19

What is a lever

Answer 19

A lever is a rigid, straight or bent bar which is capable of turning about a fixed axis/

Question 20

Principle of a lever

Answer 20

Clockwise moment of load about the fulcrum = anticlockwise moment of effort about the fulcrum

Load x Load arm = Effort x Effort arm

Question 21

What is law of levers?

Answer 21

M.A = Effort arm FA / Load arm FB

Question 22

Differentiate b/w
(i) Class I levers
(ii) Class II levers
(iii) Class III levers
based on position of fulcrum, length of EA and LA and value of M.A and V.R

Answer 22

(i) Fulcrum is b/w effort arm and load arm (does not have to be at midpt) and M.A and V.R can be = 1, <1 or >1

(ii) Fulcrum and Effort are at two ends of the lever and load is in b/w. EA>LA and M.A and V.R >1

(iii) Fulcrum and Load are at two ends and effort is in b/w and effort is in b/w. LA > ER and M.A and V.R <1

Question 23

Give two examples of each and state what type of a machine they are:
(i) Class I
(ii) Class II
(iii) Class III

Answer 23

(i) Seesaw = Force multiplier
Scissors = Speed multiplier

(ii) Nut cracker, wheelbarrow . Class II are always Force multipliers

(iii) Sugar tongs, knife. Class III are always speed multipliers

Question 24

Examples of levers in human body:

Answer 24

(i) Nodding of head is Class I
(ii) Raising weight of body on toes is Class II
(iii) Raising load by forearm is class III

Question 25

What is a fixed pulley?

Answer 25

A pulley which has its **axis of rotation stationary in position** is called a fixed pulley.

Question 26

In a single fixed pulley, M.A is _____ than 1 and V.R is _____ 1.

Answer 26

Lesser Equal to

Question 27

What is the use of a single fixed pulley?

Answer 27

It is used to change direction of effort applied, i.e to apply effort in a convenient direction

Question 28

What is a movable pulley?

Answer 28

A pulley whose axis of rotation is movable and not fixed in position is called a movable pulley.

Question 29

M.A of a single movable pulley=?

Answer 29

M.A = 2T/T = 2

Question 30

Difference between Single Fixed Pulley and Single Movable pulley (2m)

Answer 30

Single fixed pulley: 1. It is fixed to a rigid support 2. The axis of rotation does not move in space Single Movable pulley: 1.It is not fixed to a rigid support 2. The axis of rotation also moves.

Question 31

What are the two ways to make a pulley combination?

Answer 31

1. Used one fixed pulley and several movable pulleys attached to same rigid support 2. **Block and Tackle System:** Use several pulleys in two blocks out of which the upper block is fixed and lower block is movable

Question 32

G.R: The number of pulleys in the lower block is kept equal to or lesser than the number of pulleys in the upper block

Answer 32

For convenience of applying effort in the downward direction.

Question 33

Fill in the blanks: 1. The pulley system is a ________ (force / speed) multiplier. 2. For greater efficiency, the pulleys in the lower block should be as _______ (light / heavy) as possible.

Answer 33

1. Force 2. Light

Question 34

How can friction in the bearings of the pulley be minimized?

Answer 34

By using lubricants