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physICs query...
- Thread starter hassam
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hassam said:
That's a good question. It's because we assume air resistance to be acting in this case and suppose that if a body has 20J energy and when it will reach max height, due to air resistance the energy becomes 18J, and so when falling back, the less energy results in less velocity and so the time taken to return will be greater. That's the explanation told by my teacher while answering an MCQ related to it. If you've any problem with understanding my answer, then I can elaborate it, if you want me to! =)
hmm...nyc approch but wat abt this...
when ball is travelling upwards both gravity and air resistance are opposing its motion.the velocity of the object is always decreasing while going up so this means magnitude if air resistance must also decrease...lets consider this case
an object fired vert. upwards with 100 m/s velocity.we know if there is no air resistance its velocity will decrease by 10 m/s every second.now lets consider air resistance is also present.the instant at which the object was fired air resistance was not acting at all...ryt? within a second air resistance becomes operational.we know that air resistance is directly related to speed of the object.during the whole journey of the object upwards the speed will be decreasing so air resistance will be decreasing right from the point it became operational.
now consider the down trip of the object.well this time the object will be aided by gravity and its speed will increase throughout the fall so that means air resistance will increase and a point will come when it will equal to weight of object after wich the object will fall with a constant terminal velocity.
now tell me where does this expalnation take me 2?
i cant just figre out the correct anser.....nd ur expalnation is ok Xishi but hw cn we figre out the anser by this way
when ball is travelling upwards both gravity and air resistance are opposing its motion.the velocity of the object is always decreasing while going up so this means magnitude if air resistance must also decrease...lets consider this case
an object fired vert. upwards with 100 m/s velocity.we know if there is no air resistance its velocity will decrease by 10 m/s every second.now lets consider air resistance is also present.the instant at which the object was fired air resistance was not acting at all...ryt? within a second air resistance becomes operational.we know that air resistance is directly related to speed of the object.during the whole journey of the object upwards the speed will be decreasing so air resistance will be decreasing right from the point it became operational.
now consider the down trip of the object.well this time the object will be aided by gravity and its speed will increase throughout the fall so that means air resistance will increase and a point will come when it will equal to weight of object after wich the object will fall with a constant terminal velocity.
now tell me where does this expalnation take me 2?
i cant just figre out the correct anser.....nd ur expalnation is ok Xishi but hw cn we figre out the anser by this way
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@Hassam:
Well, the same questions were asked by other students when the teacher told us about it. The bar is traveling in a fluid which is Air, so while traveling both upwards and downwards it will face air resistance. It's like that you walk into a swimming pool, when you'll go forward you'll face resistance of water, and when you'll go backward again you'll face resistance. So while traveling downwards in air, the object will also face Viscous drag and going back to my previous example, the energy will decrease from 18J to 16J. So returning back to original position the object will have less Energy. It means that there's no BIG part played by gravity on object, because while going upwards and downwards, gravity will act at both times. =)
I don't know whether you'll understand it OR not, but this is the explanation. And I think I can't deliver the EXACTLY same elaboration as given by the teacher.
Well, the same questions were asked by other students when the teacher told us about it. The bar is traveling in a fluid which is Air, so while traveling both upwards and downwards it will face air resistance. It's like that you walk into a swimming pool, when you'll go forward you'll face resistance of water, and when you'll go backward again you'll face resistance. So while traveling downwards in air, the object will also face Viscous drag and going back to my previous example, the energy will decrease from 18J to 16J. So returning back to original position the object will have less Energy. It means that there's no BIG part played by gravity on object, because while going upwards and downwards, gravity will act at both times. =)
I don't know whether you'll understand it OR not, but this is the explanation. And I think I can't deliver the EXACTLY same elaboration as given by the teacher.
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@ zishi: i strongly agree with yew. the projectile would take longer to fall to its initial position, because as it rises, the force of air friction and gravity work against the velocity. While falling, only air friction opposes the velocity.
usman said:
usman according to u during upward journey: two forces r opposing and during downward journey only one force is opposing:thats exactly wat u said...ryt? so i cNt get this that how on Earth will this very fact u mentioned will cause the time for journey UP to be shorter