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Tag: class-9

Question1: State whether the following statements are true or false. Justify your answers. 

Class 9
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When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

Class 9 Physics Sound
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The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

Class 9 Physics Sound
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A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?

Sound Class 9 Physics
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What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?

Class 9 Physics Sound
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What is the audible range of the average human ear?

Class 9 Physics Sound
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An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s–1?

Class 9 Physics Sound
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State the universal law of gravitation.

Class 9 Physics
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An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 m s–2?

Class 9 Physics
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A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate: (a) the net accelerating force and (b) the acceleration of the train.

Class 9 Physics
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A stone of 1 kg is thrown with a velocity of 20 m s–1 across the frozen surface of a lake and comes to rest after traveling a distance of 50 m. What is the force of friction between the stone and the ice?

Class 9 Physics
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A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 tonnes (Hint: 1 tonne = 1000 kg.)

Class 9 Physics
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