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Taking no account of air resistance, draw an acceleration time graph of a boy on a trampoline. Starting with the boy suspended in the air dropping, bouncing off the trampoline and rising. End the graph after 2 cycles, with the boy suspended in the air as he started. Take down as positive.

Really stuck on this.

Ive come up with a constant acceleration until he hits the trampoline and then a curve of decreasing acceleration. But then nothing after that. Could some one give me some sort of quick sketch or drawing.

Thanks very much,

Varun

PS. The hint from the teacher was to take into account the elastic properties of the trampoline.

Really stuck on this.

Ive come up with a constant acceleration until he hits the trampoline and then a curve of decreasing acceleration. But then nothing after that. Could some one give me some sort of quick sketch or drawing.

Thanks very much,

Varun

PS. The hint from the teacher was to take into account the elastic properties of the trampoline.

Scroll to see replies

Consider the boy at various points in the action.

As he is suspended in the air, there is a constant downwards force (9.8ms^-2 if you need numbers) acting on him.

As he starts falling, the upwards thrust of air resistance stars canceling this out gradualy.

As he hits the trampoline, the elastic upwards force exerted by it cancels out the remaining downwards force and produces a strong upwards force over a short period.

As he bounces, the upwards force reduces again as he leaves the bed, and will be totaly replaced by a stronger than before downwards force made up of gravity and air resistance.

As he reaches the top of the bounce and slows, air resistance decreases to zero again, leaving just gravity.

That help at all? I can't manage a picture at the moment, but just plot through those points and think about what happens between them.

As he is suspended in the air, there is a constant downwards force (9.8ms^-2 if you need numbers) acting on him.

As he starts falling, the upwards thrust of air resistance stars canceling this out gradualy.

As he hits the trampoline, the elastic upwards force exerted by it cancels out the remaining downwards force and produces a strong upwards force over a short period.

As he bounces, the upwards force reduces again as he leaves the bed, and will be totaly replaced by a stronger than before downwards force made up of gravity and air resistance.

As he reaches the top of the bounce and slows, air resistance decreases to zero again, leaving just gravity.

That help at all? I can't manage a picture at the moment, but just plot through those points and think about what happens between them.

This is a trick question, kind of, it is very logical when you think about it. The acceleration acting vertically is always the same, at 9.8 ms^(-2) no matter what direction he is going.

It will be a straight line from 9.8ms^(-2) over time, as this is the only acceleration acting on him due to gravity.

A velocity-time graph would act in the way you are describing.

It will be a straight line from 9.8ms^(-2) over time, as this is the only acceleration acting on him due to gravity.

A velocity-time graph would act in the way you are describing.

The graph must conform to how the centre of mass(the boy in this case) is accelerating/decelerating over time, not the constant act of gravity. In a way, it's a bit like Simple Harmonic Motion. There will be NO acceleration at the mid-point of the interval, and NO acceleration at the extreme ends(at peak distance in the air and on the trampoline). At the extreme ends, the mass will remain stationary. From then on, acceleration will occur.

B Beth

The graph must conform to how the centre of mass(the boy in this case) is accelerating/decelerating over time, not the constant act of gravity. In a way, it's a bit like Simple Harmonic Motion. There will be NO acceleration at the mid-point of the interval, and NO acceleration at the extreme ends(at peak distance in the air and on the trampoline). At the extreme ends, the mass will remain stationary. From then on, acceleration will occur.

At the extreme ends of the vertical motion, the boy is accelerating.

Plus, this situation cannot be descibed as SHM, because the maximum speed of the motion doesn't occur in the centre of oscillation.

Widowmaker

At the extreme ends of the vertical motion, the boy is accelerating.

Plus, this situation cannot be descibed as SHM, because the maximum speed of the motion doesn't occur in the centre of oscillation.

Plus, this situation cannot be descibed as SHM, because the maximum speed of the motion doesn't occur in the centre of oscillation.

You're wrong: At the extreme ends the boy is stationary for a very short time period.

Do you have reading difficulties? I specifically said 'In a way, it's a bit like Simple Harmonic Motion'.

Is this some lame attempt to get back at me for correcting you?

B Beth

You're wrong: At the extreme ends the boy is stationary for a very short time period.

Do you have reading difficulties? I specifically said 'In a way, it's a bit like Simple Harmonic Motion'.

Is this some lame attempt to get back at me for correcting you?

Do you have reading difficulties? I specifically said 'In a way, it's a bit like Simple Harmonic Motion'.

Is this some lame attempt to get back at me for correcting you?

Have you got it in for me or something?

--------------

B Beth

You're wrong: At the extreme ends the boy is stationary for a very short time period.

Do you have reading difficulties? I specifically said 'In a way, it's a bit like Simple Harmonic Motion'.

Is this some lame attempt to get back at me for correcting you?

Do you have reading difficulties? I specifically said 'In a way, it's a bit like Simple Harmonic Motion'.

Is this some lame attempt to get back at me for correcting you?

bitch.

B Beth

Congratulations on the negative reputation(that doesn't count).

You low life geek who has nothing going for him other than his school work.

Get a life.

You low life geek who has nothing going for him other than his school work.

Get a life.

my god you're a cow.

sillylot

vertical acceleration is always constant (remember projectile motion).. its not like simple harmonic motion..

the velocity graph goes like that...

the velocity graph goes like that...

If the acceleration is constant then the vertical velocity is linearly proportional to to time. Just work it out using the usual equations.

v = u + at

Therefore the vertical speed, plotted against time, is just a straight line!!

A harmonic oscillator requires a very specific form of force, where it is non constant, and proportional to distance.

B Beth

And you need ~~to get ~~ to get laid.

It's so obvious you wern't blessed with looks and that your schooling is all you have.

I pity you.

It's so obvious you wern't blessed with looks and that your schooling is all you have.

I pity you.

Tut tut, I can be critical too.

B Beth

Resorting to grammatical inconsistencies?

You lonely person.

You lonely person.

can someone please shut this bitch up?

B Beth

Hush.

Interests:

Giving Blowjobs to horny boys

Giving Blowjobs to horny boys

Hmm, slut.

B Beth

Proud to be one.

Loner.

Loner.

lol, quote of the day.

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