A ball is thrown downward with an initial velocity of 12.1 m/s. How long will it take to reach a velocity of -24.5 m/s? (Negative indicates the downward direction) A) 1.27 s
B) 3.73 s
C) there is not enough i for to solve the problem
D) 14.6 s

Explanation:

The sig figs are off in the answer (unless you use -9.81 for the acceleration due to gravity. My classes always use -9.8, which is 2 sig figs. But nevertheless, we can solve it!) Use the velocity formula:

where vf is the final velocity, v0 is the initial velocity, a is the acceleration due to gravity, and t is the time in seconds. Filling in, using the fact that both the velocities are negative since the ball is going down:

-24.5 = -12.1 +(-9.8)t or

-24.5 = -12.1 - 9.8t and

-12.4 = -9.8t and divide to get that

t = 1.27 sec

most of them using statistics and defining how things are being measured