Question

A girl swims the length of a pool and back in 29.4 s. The pool is 21.5 m long, and the girl's speed is constant. (a) Compute her speed v and her average velocity v bar. speed average velocity (b) When is her acceleration not equal to zero? when she reaches the middle of the pool when she is turning around at the end of the pool when she is about to reach the end of the pool

Answer 1

This question is used to test your understanding about SCALAR and VECTOR concepts.
SCALAR means NOT CONSIDER the DIRECTION, SIMPLY the MAGNITUDE.
VECTOR means the description includes MAGNITUDE and DIRECTION.

So that, the first question HER SPEED is equal to the total swam distance divided by the time:
(2 x 21.5 m) / 29.4 sec = 1.462 m/S

second question, it asks for the average velocity, the GIVEN conditions:
Constant Speed, the time for forward and return should be the same = 29.4s/ 2 = 14.7 s and
each travel speed is equal to 21.5/14.7 = 1.462 m/S
But the average VELOCITY is ZERO
It is because if the forward direction is a +ve VECTOR, then the opposite return direction must be a -ve VECTOR, Sum of +1.462 with -1.462 equals to ZERO

Third question, all of the above answerer cannot give me a satisfied explanation. All of them are arguing with the question.
DON'T assume there is any STOP / ACCELERATION / DECELERATION when she made her turn.
It is because the question stated "the girl's speed is CONSTANT"
Think about that you can keep the same speed on turning your car for making a big U-turn. You simply changed the direction NOT the SPEED. So that, there is NO acceleration, it equals to ZERO.

I follow the Given information, the girl's speed is CONSTANT. When she made the U-turn, she simply changed her direction not the SPEED, so that the acceleration equals to ZERO all the time.
But when she reaches to the end of the pool, she has to stop her swimming. Even she may be stopped by crushing onto the wall, she will stop with a very big deceleration or negative acceleration