+g. We’re given v 0 , s, and a, and asked for t. So v is missing; it isn’t given and it
isn’t asked for, and we use Big Five #3.
- One second after being thrown straight down, an object is falling
with a speed of 20 m/s. How fast will it be falling 2 seconds later?
Here’s How to Crack It
Call down the positive direction, so a = +g and v 0 = +20 m/s. We’re given v 0 , a,
and t, and asked for v. Since s is missing, we use Big Five #4.
v = v 0 + at = (+20 m/s) + (+10 m/s^2 )(2 s) = 40 m/s- If an object is thrown straight upward with an initial speed of 8
m/s and takes 3 seconds to strike the ground, from what height was
the object thrown?