Acceleration on an Elliptical Path

A particle is moving on an elliptical path as shown, at a constant speed. At which point is the particle's acceleration at maximum?

A B C Same Everywhere

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5 solutions

Gautam Sharma
Aug 4, 2014

The Radius of curvature at c c is smallest.
So acceleration is v 2 R \dfrac{v^2}{R} .

Thus, the acceleration is maximized at C C .
And radius of curvature can be checked by drawing circles at A , B A, B and C C by taking small arcs around them you will get the radius of the circle drawn at is minimum.

please...let me know where i am wrong.....i used the parametric equation of ellipse:x=acos(t),y=bSin(t).. and differentiated it twice to get acceleration and it came out to be constant....u could try for yourself..any suggestions?

Archit Bohra - 6 years, 10 months ago

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Archit ur finding tangential acc. which is const.(actually zero) but u need to find normal acc.....

Gudipati Anudeep - 6 years, 9 months ago

Well I got the answer as b a \frac{b}{a} c o s e c 2 cosec^{2} t... d x d t \frac{dx}{dt} = -asin(t) and d y d t \frac{dy}{dt} = bcos(t). Now using the chain rule: d y d x \frac{dy}{dx} = d y d t d x d t \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = - b a \frac{b}{a} . c o s ( t ) s i n ( t ) \frac{cos(t)}{sin(t)} . Now we need to be more careful when working out the 2nd derivative (also I'm going to ignore the constant for now): " d 2 y d x 2 \frac{d^2 y}{dx^2} " = d d x \frac{d}{dx} [ d y d x \frac{dy}{dx} ] = d d t \frac{d}{dt} [ c o s ( t ) s i n ( t ) \frac{cos(t)}{sin(t)} ] d t d x \frac{dt}{dx} (by the chain rule). Now using the quotient rule: d 2 y d x 2 \frac{d^2 y}{dx^2} = 1 v \frac{1}{v} d u d x \frac{du}{dx} - u v 2 \frac{u}{v^2} d v d x \frac{dv}{dx} = -[ s i n 2 t + c o s 2 t s i n 2 t \frac{sin^2t +cos^2t}{sin^2t} ] = - c o s e c 2 cosec^{2} (t). Now multiplying by the constant that we neglected earlier gives: d 2 y d x 2 \frac{d^2 y}{dx^2} = b a \frac{b}{a} c o s e c 2 cosec^{2} (t)

Curtis Clement - 6 years, 5 months ago

If there is acceleration, then how can speed be constant?

Ollie Rodley - 5 years, 7 months ago

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It is not tangential acceleration it is radial.It is requires to keep body on given curve.Example when u sit on merry-go-round u experience an outward force so to balance that an inward force is required(equal in magnitude to outward force).Hence this force is not increasig speed.

Gautam Sharma - 5 years, 7 months ago

and BTW pankaj from where are you?

Gautam Sharma - 6 years, 10 months ago

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I am from Jaipur and sorry for replying late..

Pankaj Joshi - 6 years, 10 months ago

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pankaj, shouldnt the answer be C tho? since smallest radius

Justin Chan - 5 years, 2 months ago

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@Justin Chan Thanks. We have updated the answer to C.

In future, if you spot any errors with a problem, you can “report” it by selecting "report problem" in the menu. This will notify the problem creator / staff who can fix the issues.

Calvin Lin Staff - 5 years, 1 month ago

answer pankaj Are you from North Delhi.

Gautam Sharma - 6 years, 10 months ago

I thought that eclipse shape is just a point of view. But, actually its an eclipse. Poor me

Rafi Ramadhana - 6 years, 9 months ago

They should have said radial acceleration. Otherwise I understand tangential acceleration

César Balguerías Ortiz - 4 years, 10 months ago
Curtis Clement
Jan 9, 2015

acceleration = Δ v e l o c i t y t i m e \frac{\Delta\ velocity}{time} and velocity is a vector quantity (it has direction and magnitude), so as the speed (i.e.magnitude) is constant, then the Δ \Delta velocity relies on direction. C shows the sharpest turn, so that is where acceleration is greatest

They should have specified what acceleration they referred to.

César Balguerías Ortiz - 4 years, 10 months ago
Bhuvan Hikoo
Jul 24, 2014

to maintain constant speed, at higher distance more acceleration is required , c is at higher distance so it is answer.

But by comparing equation of centripetal force=centrifugal force So the account. To equation a=v^2/r Where r is small a is max.

bhavesh pariyani - 6 years, 10 months ago

what?????

what about if its horizontal? think

Gautam Sharma - 6 years, 10 months ago

i used the parametric equation of ellipse:x=acos(t),y=bSin(t)....that gives costant acceleration..any suggestions?

Archit Bohra - 6 years, 10 months ago

i did not undrstnd

Panshul Rastogi - 6 years, 10 months ago

In general, there are two types of acceleration according to how they affect speed. If the acceleration is perpendicular to the velocity it affects the direction but never the magnitude (speed) and if it is parallel (or tangent) to it, it affects the magnitude but never the direction. Every acceleration that affects both can be thought of as a combination of those.

Tangent acceleration is defined as the rate of change of the magnitude of the velocity, while the centripetal (perpendicular) acceleration turns out to be equal to the velocity squared times the curvature or the velocity squared over the radius of curvature.

The answer is C, because the radius of curvature is smaller there

Jaivir Singh
Aug 30, 2014

BECAUSE RADIUS AT C IS MINIMUM

why did i get b as the answer then?

Justin Chan - 5 years, 2 months ago

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Thanks. We have updated the answer to C.

In future, if you spot any errors with a problem, you can “report” it by selecting "report problem" in the menu. This will notify the problem creator / staff who can fix the issues.

Calvin Lin Staff - 5 years, 1 month ago

1 pending report

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