Two students. A and B, leave LIU together, walking down Flatbush Ave to Atlantic

Question

Two students. A and B, leave LIU together, walking down Flatbush Ave to Atlantic Terminal. Two minutes into the trip, student A stops for 3 minutes to buy coffee at Starbucks, while student B continues walking. Student A then catches up with student B. 2 minutes after leaving Starbucks, but he doesn't see Student B and passes right by her. The graph below shows the positions of the students, labeled A and B, as a functions of time. Seven minutes in to the trip (at t = 7 min), are the velocities of the students equal? If not, which is larger? For the first 7 minutes of the trip (from t = 0 to t = 7 min), are the average velocities of the students equal? If not, which is larger? For the time between t = 1 min and t = 3 min is the average acceleration of student A positive, negative, or zero? For the time between t = 1 min and t = 3 min is the average acceleration of student B positive, negative, or zero?

Explanation / Answer

a)

No, velocities are not equal at t=7 m.

velocity of A is greater than B.

The slope of the curve gives the velocity.

Slope of A is greater than B at t = 7 . So, velocity of A > B

b)

Average velocities are equal

As the total distance traveled is same for both along with the same time

c)

Average acceleration = (final velocity - initial velocity)/time

Now, final velocity of A at t=3 = 0 <---- slope =0

initial velocity = some +ve value

So, avg acceleration = (0 - (+ve))/2 = -ve value

So, avg acceleration is negative

c)

For B final velocity and initial velocites are same <----- same slope at both points

So, average acceleration = 0

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