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Old Sep 5th 2016, 04:49 PM   #1
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AP Physics

Please help
Lisa is late for the school bus. As Otto is pulling away with a constant acceleration of 1.07 m/s/s, Lisa is still 11.0 meters away, running at her top constant speed of 5.01 m/s. When will Lias catch the bus? Where will Lisa catch the bus?
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Old Sep 5th 2016, 05:07 PM   #2
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Have you made any attempt on this yourself?
As Otto is pulling away with a constant acceleration of 1.07 m/s/s
Since the bus starts with speed 0, its speed after t seconds is 1.07t m/s. Taking the position of the bus-stop to be x= 0, the busses position after t seconds is x= 0.535t^2.

Lisa is still 11.0 meters away
So Lisa's initial position (assuming the bus is moving away from her rather than toward her) is y(0)= -11.0.

running at her top constant speed of 5.01 m/s.
So her position, relative to the but stop, after t seconds is y(t)= 5.01t- 11.0.

When will Lias catch the bus?
She will catch the bus when her position is the same as the position of the bus:
x= y or 0.535t^2= 5.01t- 11.0. Solve 0.535t^2- 5.01t+ 11.0= 0. The quadratic formula is probably the simplest method.

Where will Lisa catch the bus?
Set t equal to the value you just got in either of the x and y equations above.
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