Question

The velocity of a ball as it is thrown up is 20 meters/second. It attains zero velocity after 3.5 seconds. What is the average acceleration of the ball during its upward flight? A. 5.7 meters/second B. 0.57 meters/second C. -0.57 meters/second2 D. -5.7 meters/second2 E. 5.5 meters/second2

Answer 1

The average acceleration is

$\bar a=\dfrac{\Delta v}{\Delta t}=\dfrac{0\,\frac{\mathrm m}{\mathrm s}-20\,\frac{\mathrm m}{\mathrm s}}{3.5\,\mathrm s-0\,\mathrm s}=-5.7\,\dfrac{\mathrm m}{\mathrm s^2}$

so the answer is D.

Answer 2

Average acceleration = (change in speed) / (time for the change)

If a ball is thrown upwards at a speed of 20 m/s, and reaches the top of its arc with zero speed after 3.5 seconds, then its average acceleration is

(0 - 20 m/s) / (3.5 s) =

(-20 m/s) / (3.5 s) =

-5.71 m/s² .

Note: This could not be happening on Earth, and there's no planet or other body in our solar system with a gravitational acceleration anywhere near that number.