A basketball rolls off a deck that is 3.2 m from the pavement. The basketball lands 0.75 m from the edge of the deck. How fast was the basketball rolling? Seema lists the given values in a chart and determines that the unknown value is vx.

given: value:

change in y 3.2m

ay - 9.8 m/s2

change in x 0.75m

Which describes Seema's error?

A. The y and x values are switched.

B. The unknown is, not vx.

C. The value for ay is not known.

D. The value of y should be - 3.2 m.

The table is almost perfect. BUT ... since she called ay negative, that means she's calling the upward direction positive-y and the downward direction negative-y. In that case, since the ball moves downward from the deck to the pavement, the change in y should be negative 3.2 m. Everything else in her table is fine. Choice-D is the good one.

Now, regarding the speed of the ball ...

How long does it take to fall 3.2 m?

Use the formula. D = 1/2 g T^2.

3.2 = 4.9 T^2.

T^2 = 3.2/4.9

T = √ (3.2/4.9) = 0.808 second.

The ball hit the pavement 0.808 second after it rolled off the deck. So that's also the time it took to move the 0.75 m horizontally.

Speed = distance / time

Speed = 0.75 m / 0.808 second

Speed = 0.928 meter/second.

The y and x values are switched. So, the answer is A. This is because the basement to pavement distance is horizontal (x), and y is the vertical distance or when the ball rolled off.