03: Machine : Icse-x-physics

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ICSE-X-Physics

03: Machine

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Exercise 3 A

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Section : I
Numericals

Qstn #1
A Woman draws water from a well using a fixed pulley. The mass of bucket and water together is 6 kg. The force applied by the woman is 70 N. Calculate the mechanical advantage. (Take g = 10 m s^-2)
Ans : 1 The force applied by the women is = 70 N.The mass of bucket and water together is = 6 kgTotal load = 6 × 10 = 60 NMechanical advantage M.A = Load/Effort = 60/70 = 0.857

Qstn #2
A fixed pulley is driven by a 100 kg mass falling at a rate of 8.0 m in 4.0s. It lifts a load of 500 kgf.
Ans : 2 Load = 500 kgfMass of falling object = 100 kgDisplacement of effort = 8.0 mTime taken = 4.0s

#2-a
Calculate the power input to the pulley taking the force of gravity on 1 kg as 10 N.
Ans : Effort = 100 X 10 = 1000 kgfPower Input = (displacement x effort)/time= (8 × 1000)/4= 2000 W

#2-b
If the efficiency of the pulley is 75%, find the height to which the load is raised in 4.0s.
Ans : The efficiency of the pulley is = 75% = 0.75Mechanical advantage of this system M.A = Load/Effort = 500/100 = 5Velocity ratio of this system V.R = M.A/η = 5/0.75 = 20/3Displacement of load D = displacement of effort /V.R. = (3 × 8)/20 = 1.2 m

Qstn #3
In a block and tackle system consisting of 3 pulleys, a load of 75 kgf is raised with an effort of 25 kgf. Find: (i) the mechanical advantage, (ii) velocity ratio and (iii) efficiency.
Ans : 3 Load = 75 kgfEffort = 25 kgfn = 3MA = Load/Effort = 75/25 = 3or MA = n = 3velocity ratio VR = n = 3Efficiency η = M.A/V.R = 1 or 100%

Qstn #4
In fig. draw a tackle to lift the load by applying the force in the downward direction. Mark the position of load and effort.
Ans : 4

#4-a
If the load is raised by 1 m, through what distance will the effort move?
Ans : The effort move = 1 × 5 = 5m

#4-b
State how many strands of tackle are supporting the load?
Ans : Five strands of tackle are supporting the load.

#4-c
What is the mechanical advantage of the system?
Ans : Mechanical advantage of the system = M.A = Load/effort = 5T/T = 5

Qstn #5
A block and tackle system has 5 pulleys. If an effort Of 1000 N is needed in the downward direction to raise a load of 4500 N, calculate:
Ans : 5 A block and tackle system has 5 pulleys. (n = 5)Effort = 1000 NLoad = 4500 N

#5-a
the mechanical advantage
Ans : The mechanical advantage M.A = load/effort = 4500/1000 = 4.5

#5-b
the velocity ratio, and
Ans : The velocity ratio = n = 5

#5-c
the efficiency of the system
Ans : The efficiency of the system η = M.A/V.R = 4.5/5 = 0.9 or 90%