עמוד:39

7 . A dial clock was operated using an electric battery . a . Describe the changes occurring in the energy . b . Three years passed and the clock stopped . Does this contradict the law of conservation of energy ? Explain . 8 . Amir told Dana : “ Last Saturday we drove to some relatives and then returned home . Throughout the entire trip , the car was travelling on a flat plain , without climbing or descending . In other words , it neither gained potential energy nor gained kinetic energy ( since it ultimately returned to its point of departure ) . Thus , chemical energy was lost ( through the burning of fuel in the car’s engine ) . This contradicts the law of conservation of energy . ” Dana answered : “ There is no contradiction of the law of conservation of energy here . ” Which one of them is right ? Explain . 9 . A child slides down a slide and while sliding , due to friction with the slide , part of his kinetic energy is converted to heat . The yellow color represents kinetic energy ; the blue – potential energy ; the red – heat . a . Which of the following charts correctly describes the boy’s energy in each of the following states ? Explain . 1 . In the middle of the way down . 2 . Immediately after reaching the ground and stopping . b . What remains constant in the energy transformation process ? How is it represented ? 10 . A weight is tied by a string to a nail on the wall and is used to move a small four-wheeled cart . After lifting the weight , it is released and strikes the cart . The cart moves forward and then comes to a stop after traveling a certain distance . a . Describe the changes in energy from the moment the weight is released until the cart comes to a stop . b . What can be done so that the cart travels as far as possible after being struck by the weight ? You may change anything you want – the cart’s wheels , its shape , the weight itself , and so on . You may also use anything you want , such as oil , and so on . Explain how your actions increase the cart’s travel distance .

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