Question

which of the following correctly describes the velocity and acceleration of the object after 4s?

Answer 1

Answer:

C

Explanation:

The acceleration will be negative, as in the problem statement, the upwards direction is defined as positive (the object is shot upwards and has a positive velocity), so immediately, we can eliminate A and B.

You can then use the kinematics equation:

$v=v_o+at$, where

a= -9.8 m/s^2 (acceleration due to gravity)

t= 4 s (time)

v$_0$= 20 m/s (initial speed)

when you solve, the final velocity is -19.2 m/s, so the velocity is negative (the object is on its way down).