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प्रश्न
उत्तर
K.E ,K = `1/2`mv²
If speed is doubled;
K.E , K = `1/2` m (2v)²
or K' = 4 x `1/2` mv² = 4K
Thus K.E becomes four times
Thus if initially the K.E is 5J after increasing the speed twice, its k.E will become 4 x5 = 20 J.
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संबंधित प्रश्न
Look at the activity below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
A sailboat is moving due to wind energy.
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- A boy pushing a heavy rock
- A boy climbing up the stairs
- A coolie standing with a box on his head
- A girl moving on the road.
Define 1 joule of energy.
A boy weighing 25 kgf climbs up from the first floor at height 3 m above the ground to the third floor at height 9m above the ground. What will be the increase in his gravitational potential energy? (Take g = 10 N kg -1)
What happens to the work done when the dispacement of body is at right angles to the direction of force acting on it? Explain your answer.
P, Q and R are three forces which act as shown in fig.
The point O lies in the same plane. Given, P = Q = R = 10N
(i) Which force has the least moment about O? Give a reason.
(ii)Which force has the greatest moment about O? Give a reason.
What is the work done against gravity when a body is moved horizontally along a frictionless surface?
On what factors does the work done by a force depend?
Complete the following sentences:
Joule is the unit of .......
What do you understand by 'potential energy' and 'Kinetic energy'? Give three examples of each to illustrate your answer.
Fill in the boxe to show the corresponding energy transformation.
Fill in the boxe to show the corresponding energy transformation.
State the energy changes which take place when Water stored in the dam is used to turn turbine in dynamo.
Give an example
Electrical energy changes of sound energy.
What are the advantages and disadvantages of using solar cells for producing electricity?
A girl of mass 40 kg runs a height of 80 stairs, each 25 cm high with a load of 20 kg on her head in 25 sec. If g is 10 m/s2, find:
(i) Gravitational force acting on the girl.
(ii) Work done by her.
(iii) Useful work done by her.
(iv) Her power in watt.
