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Questions
State two functions of a machine.
State true functions of machine.
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Solution
Various functions that a machine can perform are:
- Changing the direction of applied force – Example: When a flag is hoisted with the help of a pulley.
- Changing the magnitude of applied force – Example: Bottle opener multiplies the applied force and much less effort is required to open the cap.
- Applying force at a convenient point – Example: In a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
- Changing the speed of an object – Example: While riding a bicycle, force is applied on pedals which multiplies the speed.
RELATED QUESTIONS
A boy uses a single fixed pulley to lift a load of 50 kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer.
A pulley system has three pulleys. A load of 120 N is overcome by applying an effort of 50 N. Calculate the Mechanical Advantage and Efficiency of this system.
Explain the working of a gear system.
Explain how a gear system can be used to obtain Change in direction of rotation. Given one example.
Name the type of single pulley that can act as a force multiplier. Draw a labelled diagram of the pulley mentioned by you.
In which direction does the force need to applied, when a single pulley is used with a mechanical advantage greater than one? How can you change the direction of force applied without altering its mechanical advantage? Draw a labelled diagram of the system.
Draw a diagram of a combination of three movable pulleys and one fixed pulley to lift up a load. In the diagram, show the directions of load, effort and tension in each strand. Find:
- mechanical advantage,
- Velocity ratio and
- efficiency of the combination in ideal situation.
Give reason for the following:
In a single fixed pulley, the velocity ratio is always more than the mechanical advantage.
The diagram below shows a pulley arrangement :
(i) Copy the diagram and mark the direction of tension on each strand of the string.
(ii) What is the velocity ratio of the arrangement ?
(iii) If the tension acting on the string is T, then what is the relationship between T and effort E ?
(iv) If the free end of the string moves through distance x, find the distance by which the load is raised.
Give a reason for the following:
In a single fixed pulley, the velocity ratio is always more than the mechanical advantage.
Name a machine which is used to:
change the direction of force applied.
In the case of a block and tackle arrangement, the mechanical advantage increases with the number of pulleys. Explain.
What is the relation between the mechanical advantage and the number of strands of string used to support the load, in a ‘block and tackle’ set-up?
What is a block and tackle system of pulleys? What precautions would you observe while rounding the string so that the effort is applied in the downward direction?
The pulley system shown in the figure is to be used to lift a load W. If the man applying the effort cannot apply a force exceeding 1000 N, what is the maximum load that can be lifted?
The actual load that the man is finally able to lift turns out to be 2700 N. What are the values of the actual M.A., obtained, and the efficiency of the actual set-up?
If the weight of the movable pulley is W, obtain the expression for MA, VR, and efficiency.
A ‘block and tackle’ system used 3 pulleys in the lower block and 4 pulleys in the upper block. What is the ‘velocity ratio’ of this system? If the load is to be lifted by a person capable of applying a maximum effort of 1000 N, what is the maximum load than can be lifted under ideal conditions?
The actual maximum load that gets lifted turns out to be 6300 N. What are the values of the actual M.A. and efficiency of the set-up?
Name the type of single pulley that has an ideal mechanical advantage equal to 2. Draw a labelled diagram of the pulley mentioned by you.
