A rock dropped from a tall building. After falling for 10 seconds, it reaches a speed of 98 meters/second. At what rate was the rock accelerating?

A) 9.8 m/s^2
40 m/s^2
C) 102 m/s^2
D) 157 m/s^2

I got a.

2) an xray machine consumes energy at the rate of 50 watts. How many joules of energy does it consume in 1 second?

A) 350 j
50
C) 900 j
D) 11.7 j

I got a


Would appreciate it if you could explain as well. Thank you guys.

For A, use kinematics equations

final velocity = intitial velocity + acceleration * time

98 = 0 (it was dropped from rest after all) + (-9.8)(t)

-10 m/s^2.......A would be your answer, my guess is they assume 10 for g

(You can shortcut this one if you realize than -9.8 is acceleration due to gravity, it only changes once you get far from earth)

For B, remember a watt is a joule per second

That.....kind of answers the question! Damn, easier than we thought. (50 joules)

This post was edited by Casey on Sep 16 2015 04:11am