A) mechanical advantage. 2 5
B) effort required if load lifted is 1000 kgf. 416.67 kgf
2) A boy lifts a load of 400N through a vertical height of 5m in 10s by a fixed pulley by applying an effort of 480 N at the other end. Find:
A) velocity ratio. 1
B) mechanical advantage. 0.833
C) efficiency. 83.3%
D) energy gained by the load. 2000J
E) power developed by the boy. 240 watt
F) what is the justification in using the pulley ? To change the direction of the force applied in a convenient direction.
3) A handle of a nutcracker 16cm long and a nut is placed 2cm from its hinge. if a force of 4 kgf is applied at the end of handle to crack nut, what weight if simply placed on nut will crack it? 32 kgf
4) Find the length of a power arm(effort) of a lever required to raise a load of 20p kgf kept at a distance of 1m from the fulcrum. If the power applied is 20 kgf, also calculate its M. A. 19m, 10
5) A lever in the form of a bar is 1 m long. A load is suspended from one end of the bar. The falcrum is 30 cm from the centre of gravity of the bar which is at the centre of the bar. The effort is applied at the other end. Find the velocity ratio. why the lever formed by is not 100% efficient? 4, 0.25, For a 100% efficient machine, the mechanical advantage is numerically equal to the velocity ratio. Here, in this case, the mechanical advantage is less than the velocity ratio, Hence, the bar is not 100% efficient.
6) Calculate the:
a) velocity ratio. 6
b) mechanical advantage. 5
c) percentage efficiency. 83.33%
of a machine which overcomes a resistance of 800N through a distance of 0.12m, when an effort of 160N acts through a distance of 0.72m.
7) An effort of 500N is applied through 0.5 m on a machine, whose efficiency is 90%, such that resistance is overcome through 0.04m. Calculate
A) velocity ratio. 12.5
B) mechanical advantage. 11.25
C) resistance overcome by the machine. 5625 N,
8) A crow bar of length 2.0 is used as a machine, to lift a box of 100 kgf by placing a fulcrum at a distance of 0.1m from the box. Calculate
A) velocity ratio. 10
B) effort required. 5.26 kgf
What assumption has been made to you in solving the problem? Assumption: No effort is wasted in overcoming friction.
9) A uniform plank of sea-saw is 5m long and supported at its centre. A boy weighing 40 kg sits at a distance of 1.5 m from one end of see-saw. Where must a girl weighing 25 kg sit on the other end of the sea-saw, so as to balance the boy? 0.9 m
10) A pulley system has a velocity ratio 3 and an efficiency 80%. Calculate the mechanical advantage of the system and the value of the effort required to raise a load of 300 N. 2.4,125N
11) A fixed Pulley is driven by a 100 kg mass falling at a rate of 8.0m in 4.0s. It lifts a load of 500 kgf. Calculate the power input to the pulley taking the force of gravity on 1 kg as 10N. If the efficiency of the pulley is 75%, find the height to which the load is raised in 4.0s. 1500W, 1.2m
12) An effort of 240N overcome a useful load of 1000 B when applied on a block and tackle system of pulleys, such that weight of movable block and friction is 200N. Calculate the:
A) Mechanical advantage. 4.16
B) velocity ratio. 5
C) total number of pulleys in the system. 5
D) efficiency of the system. 83.2%
13) A crow -bar 4m long has its fulcrum 50cm from one end. What minimum effort is required to displace a weight of 500 kgf ? Calculate the M. A. of the crow-bar. 71.43 kgf, 7
14) A pulley system has five pulleys in all and is 90% efficient. Calculate the:
A) mechanical advantage. 4.5
B) effort required to lift a load of 1000 N. 222.2N
C) resistance due to movable parts of machine and friction. 111.1N
15) A pulley system can lift a load of 1200 N by an effort of 250 N. If the resistance due to weight of movable parts and friction is 300N, calculate the:
A) mechanical advantage. 4.8
B) velocity ratio. 6
C) total number of pulleys in the system. 6
D) efficiency of the system. 80%
16) In a block in tackle system, a load of 7.5 kgf is raised with an effort of 2.5 kgf. If there are three pulleys in the system, find M.A, V.R and efficiency. 3, 3, 100%
17) A block and tackle system has 5 pulleys. If its efficiency is 60%, find the pull required to lift a load of 600 kgf. 200 kgf
18) A block and tackle system has a velocity ratio 3. A man can exert a pull of 200 kgf. What is the maximum load be can raise with this pulley system it its efficiency is 60%. 360 kgf
19) A cook uses a 'fire tong' of length 28cm to lift a piece of burning coal of mass 250g. If he applies his effort at distance of 7 cm from the fulcrum, what is the effort in S. I. unit ? (g= 10 m/s). 10
20) A woman draws water from a well using a fixed pully. The mass of the bucket and water together is 6.0 kg. The force applied by the woman is 70 N. Calculate the mechanical advantage.(g=10 m/s). 0.86
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