shown in figure).
[PUBG गेम के खिलाफ अभियान।
मोबाइल स्क्रीन के ज्यादा लंबे समय तक प्रयोग करने से बच्चों की दृष्टि पर विपरीत
असर पड़ता है। इसके लंबे समय तक प्रयोग करने से बच्चों में सुस्ती आती है। सिरदर्द होता
है। ऐसे व्यक्ति जिनको PUBG गेम की लत लग जाती है वे सामाजिक संबधों से दूर होने की
वजह से कुंठा का शिकार हो जाते हैं।
इसके खिलाफ सामाजिक जागरुकता फैलाने के लिए दिल्ली के एक स्कूल ने PUBG
गेम के खिलाफ अभियान की शुरुआत की। जिसके लिए बच्चों को आयताकार बोर्ड बनाने को
कहा गया। (चित्र देखें)
Y
D (2,6)
C(8,6)
BAN PUBG
B(8,2)
A (2,2)
x
x x
YI
Answers
Answer:
I can't understand.....,......
Answer:
Q11. What is the work done by the forge of gravity on a satellite moving around the earth? Justify your answer.
Ans. As the force acting on the body is perpendicular to the direction of displacement, .•. Work done is zero.
Q12. Can there be displacement of an object in the absence of any force acting on it? Think Discuss this question with your friends and teacher.
Ans. If an object is in a state of motion, then as per Newton’s first law of motion in the absence of any external force acting on it, the object will maintain its motion along a given straight line. So the object will have displacement. However, if the object is initially at rest then there can be no displacement, the work done by person is zero.
Q13. A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
Ans. Work is said to be done when force is applied on a body and the body shows the displacement. In this case force is applied on hay bundle but there is no displacement of it. Hence no work is said to be done on the hay.
Q14. An electric heater is rated 1500 W. How much energy does it use in 10 hours.
Ans. Power = 1500 W → 1.5 kW
time = 10 hour
Energy = ?
Energy = Power × Time taken
= 1.5 × 10
= 15 kWh
∴ Energy required = 15 kWH
Q15. Illustra.te the law of mnservation of energy by discussing the the energy changes which occur when we draw a pendulum bob to one side and allow. it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
Ans.
Let be the mean position of pendulum. When it is raised to point ‘B’ and released, it starts oscillating from B to A, A to C and back to A. It repeats this motion again and again.
At point B and C, height of pendulum is maximum, hence the potential energy at these points is maximum.
During oscillation, when pendulum moves from B – A – C, its maximum speed is at A, hence the maximum kinetic energy is at A, and potential energy at this point is minimum.
This shows the potential energy at B is transformed to kinetic energy at A and again this energy is transformed into potential energy at C.
This transformation of energy goes on and the pendulum oscillates, it does not violate the law of conservation of energy.
Bob comes to rest because there are three forces acting on it,
(i) Gravitational force exerted by earth ‘g’ which .es to bring the bob at rest.
(ii) Air resistance force that acts opposite the motion of pendulum.
(iii) Restoring force, the pendulum is tied at a point, the upward tension pull also tries to get the pendulum to its original position.
Q16. An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest.
Ans. The mass of the object = m
Velocity = v
This is the energy of the object with which the body is moving, hence same amount of energy is required to stop the boby.
∴ Work done on the object in order to bring the object to rest
Q17. Calculate the work done required to be done to stop a car of 1500 ky mouir at a uelocity of 60 1/h
Ans. mass = 1500 kg
Q18. In each of the following a force, F is acting on an object of mass m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.
Ans. (a) In case (a), the force F is perpendicular to the displacement, hence work done = 0.
(b) In case (b), the force F is in same direction as that of displacement, hence work done is positive.
(c) In case (c), the force F is opposite to the direction of displacement, hence work done is negative.
Q19. Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Ans. Yes, when several forces are acting on a body, if the forces are opposite to each other, the acceleration produced can be zero.
Q20. Find the enemy in kwh consumed in 10 hours by four devices of power 500 W each
Ans. Power = 500 W = 0.5 kW
time = 10 hours
Devices = 4
∴ Energy consumed in kWh = 0.5 kW × 10 hours × 4
=20 kWh
Q21. A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?
Ans. When a body is freely falling the energy remains conserved. Potential energy is transformed into kinetic energy. But when the by