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प्रश्न
In what way does an ‘Ideal machine’ differ from a ‘Practical machine’?
उत्तर
Ideal machine has 100% efficiency i.e., work done on the machine = work done by the machine.
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संबंधित प्रश्न
A body, when acted upon by a force of 10 kgf, moves to a distance 0.5 m in the direction of force. Find the work done by the force. Take 1 kgf = 10 N.
A boy of weight 40 kgf climbs up the 15 steps, each 15 cm high in 10 s and a girl of weight 20 kgf does the same in 5 s. Compare:
- the work done, and
- the power developed by them. Take g = 10 N kg-1.
MULTIPLE CHOICE TYPE
In an electric cell which in use, the change in energy is from:
State the SI unit of work.
Fill in the blank with suitable word :
1 joule is the work done when a force of 1 __________ moves an object through a distance of one __________ in the direction of __________.
What are the quantities on which the amount of work done depends? How are they related to work?
A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done : by the force applied by the boy?
(a) by the force applied by the boy?
(b) by the gravitational force of earth?
A girl weighing 400 N climbs a vertical ladder. If the value of g be 10 m s−2, the work by her after climbing 2 m will be :
How many watts equal one horse power?
Name the physical quantity whose SI unit is Nm.
Does the earth move around the sun with a uniform velocity?
List any six forms of energy and write a short note on each of them.
Define force. Is force a scalar or a vector quantity?
In the following case write yes, if the work is being done and no if no work is being done.
A coolie standing with a heavy load on his head
Explain, why submarines are able to dive underwater as well as a sail on the surface of the water?
A coolie is pushing a box weighing 1500 N up an inclined plane 7.5 m long on to a platform, 2.5 m above the ground.
(i) Calculate the mechanical advantage of the inclined plane. (ii) Calculate the effort applied by the coolie.
(iii) In actual practice, the coolie needs to apply more effort than what is calculated. Give one reason why you think the coolie needs to apply more effort.
Look at the activity below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
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