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#1 2007-10-05 23:52:02

Alan442
Guest

Kinematics

A car, moving with uniform acceleration along a straight level road, passes points A and B when moving with speed 30 ms-¹ and 60ms-¹ respectively. Find the speed of the car the instant it passes C, the mid-point of AB (model the car as a particle)

Thanks.

#2 2007-10-06 01:58:35

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

Re: Kinematics

Alan442 wrote:

A car, moving with uniform acceleration along a straight level road, passes points A and B when moving with speed 30 ms-¹ and 60ms-¹ respectively. Find the speed of the car the instant it passes C, the mid-point of AB (model the car as a particle).

Let the acceleration be a and the distance between A and B be d. ∴

Now let the speed at C be v. Using the same equation of motion

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#3 2007-10-07 07:25:20

HallsofIvy
Guest

Re: Kinematics

Oh, dear!  I had come to an answer of 45 mph and then realized that would be the speed when the car was at the midpoing in TIME between when it was doing 30 mph and 60 mph.  Jane is completely correct- that is the speed at the midpoint in DISTANCE between A and B.

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