IIT JEE , AIEEE Forum - Physics , Mechanics - Work energy question.(Again a LOTS question)

tarinbansal

You release an object from rest from a high altitude. If air resistance is considered, the curve that best represents the kinetic energy of the body as a function of the distance fallen is

The options are given in the figure-

Ans-3

My doubt is that at s=o, K=max. But we released the object without giving it any initial velocity. Therefore K at s=0 should be zero.

shikharbaid

i agree with u..

the body should have max ke just before touching the ground.

at rest it should have max PE

tarinbansal

Somebody please reply.

chetan_kp

according to your answer "s" should be considered as altitude

spideyunlimited

according to me it should be 2.
and it bends that specific way because in actuality when a body falls from a high altitude then after falling a certain height it attains a terminal velocity due to presence of air resistance and velocity doesn't increases further.. (just like in the case of liquids... we have that practical experiment in 11th physics - viscosity in glycerine)

tarinbansal

Ya spidey,
your point looks to be pretty good.
It was a question in Locus Online Test Series.
I have copied the same question and answer as it is.
So either we should consider the answer given to be wrong or someone please see to this question.

waterdemon

No dude,
The answer there is correct.
See the "s" there in the graph is positive x axis
So if object is falling down it means that distance at that Height.
is maximum and when it comes down it is minimum.

And "S" is mentioned it is not "H".
S = Displacement
H = Height
I think you must makeover the difference.

So graph is right.
Ans:(c)

Cheers!!!@@@!!!

Cheers!!!!!@@@!!!!!!!!

spideyunlimited

i think hes right.
but i can only understand it by relating it to examples.
like the lead ball we used to drop into the glycerine jar in the physics lab experiment of viscosity. the ball used to move fast at first and slowly its speed decreased upto a point of terminal velocity. yup water demon is right... kinetic energy is decreasing with distance covered.

tarinbansal

Waterdemon,
In the question it is mentioned that ''s'' is the distance fallen.
Which means that at s=0 object was at max height which is the position of releasing the object.
You have taken s to be height above the ground.

tarinbansal

I know the kinetic energy will decrease as the object comes down but my doubt is that according to the graph at max height, KE=max.
Why is it so when we have not provided any initial velocity to the object?

waterdemon

Yup,
If it is mentioned that S = Distance fallen.
Then it has got to be (b).
The answer mentioned is definitely wrong.

Cheers!!!!!@@@!!!!!!!

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