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CBSE Class 9 Answered

sir when we are calculating the relative velocity of car B W.R.T car A  why we have taken velocity of car b as positive   
Asked by dharmenderbudhiraja055 | 26 Jun, 2020, 05:37: PM
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V e l o c i t y space o f space B space w r t space A space equals V subscript B A end subscript equals stack V subscript B with rightwards arrow on top minus stack V subscript A with rightwards arrow on top H e r e space w e space a r e space f i n d i n g space h o w space f a s t space i s space B space w i t h space r e s p e c t space t o space A. thin space T h i s space d o e s space n o t space m e a n space t h a t space v e l o c i t y space o f space A space i s space t a k e n space a s space n e g a t i v e
Here in the figure both A and B are moving in the same direction. But B is moving faster than A . So the relative velocity of B with respect to A 
V subscript B A end subscript equals stack V subscript B with rightwards arrow on top minus stack V subscript A with rightwards arrow on top V subscript B A end subscript equals 14 minus 10 equals 4 m divided by s
Answered by Utkarsh Lokhande | 29 Jun, 2020, 10:58: AM

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CBSE 9 - Physics
An object of mass 1kg is falling from the height h=10m.calculate a) the total energy of an object at h=10m b) potential energy of the object when it is at h=4m c) kinetic energy of the object when it is at h=4m d) what will be the speed of the object when it hits the ground
Asked by mailtoparvathyprajith | 08 Feb, 2024, 06:45: PM
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CBSE 9 - Physics
1)state energy conversion takes place in hydroelectric power plants? 2)an object of mass 1kg is falling from a height of 10 m. Calculate i) the total energy of object at h=10m ii) Potential energy of an object when h=4m   3)Name energy transfers which occurs when a)an electri bell rings b)someone speake into a microphone c)there is a picture on television screen d)A torch is on  
Asked by mailtoparvathyprajith | 08 Feb, 2024, 12:32: PM
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CBSE 9 - Physics
Why do we feel light on our feet when standing in a swimming pool with water up to our armpits ?
Asked by mailtoparvathyprajith | 08 Feb, 2024, 12:13: PM
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CBSE 9 - Physics
The average speed of a moving body can never be zero but the average velocity of a moving body can be zero. Justify.
Asked by mailtoparvathyprajith | 06 Feb, 2024, 09:50: PM
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CBSE 9 - Physics
  Arrange the following speeds in increasing order(keeping the least speed first): (i) An athlete running with a speed of 10m/s. (ii) An bicycle moving with a speed of 200m/min. (iii) An scooter moving with a speed of 30km/h
Asked by mailtoparvathyprajith | 06 Feb, 2024, 09:10: PM
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CBSE 9 - Physics
3)A body does 20 joules of work in 5 seconds what is power
Asked by mailtoparvathyprajith | 06 Feb, 2024, 09:00: PM
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CBSE 9 - Physics
when an arrow is shot from its bow it has kinetic Energy. From where does it get the kinetic Energy
Asked by mailtoparvathyprajith | 06 Feb, 2024, 08:44: PM
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CBSE 9 - Physics
If person A reaches the 2nd floor Of a shopping mall by lift and Person B reaches the same floor by stairs and both their masses are same. Is work done by person B is greater than Person A  against gravitational force.Justify your answer
Asked by mailtoparvathyprajith | 06 Feb, 2024, 08:24: PM
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CBSE 9 - Physics
calculate the amount of work required to stop a car of 1000kg moving with speed of 72km/h
Asked by sadhanaasadhanaa67 | 04 Feb, 2024, 12:27: PM
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CBSE 9 - Physics
(3 X 3 = 9) CASE STUDY QUESTION 26. Ultrasounds can be used to detect cracks and flaws in metal blocks. Metallic components that are generally used in construction of big structures like buildings, machines and also scientific equipment. The cracks or holes inside metal blocks, which are invisible from outside, reduce the strength of the structure. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of flaw or defect. Clearly indicated in the figure Defect or flaw Ultrasound Detectors Metal Block (a) The transmitter sends an ultrasound wave of speed 5960m/s through a long steel bridge and a block reflects it back after 0.02s. how far the block in the metal bridge is from the transmitter. (b) With the above property of ultrasound waves, Can ultrasonic waves be used in the medical field? If so, how and give one use in the medical field to justify your answer? (c) Give two practical applications of reflection of sound waves?
Asked by mailtoparvathyprajith | 31 Jan, 2024, 06:55: PM
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