of any equations used, the numerical values substituted for the variables, and the final answer
units. Take g = 9.80 m/s2 for the gravitational acceleration when needed (1) You drop a rock and
allow it to fall toward the ground from a height of 25 meters. (a) (10 points) How long will it
take to reach the ground? (b) (15 points) One second after you drop the rock, you throw an apple
vertically downward from the same height, but with an initial speed vo. What initial speed vo
will cause the apple to hit the ground at the same instant as the rock?
Solution
a)
From
Y=Y o + V o t -(1/2)gt 2
Since rock hits the ground finally Y=0
and initial velocity is zero V o =0
0=25+0-(1/2)(9.8)*t 2
t=2.25877 s
b)
Here t=-2.25877-1=1.25877 s
=>0 =25 +V o *(1.25877) -(1/2)*9.8*1.25877 2
V o =-13.7 m/s