Mastering Phyiscs
Some Chapter 2 Questions
Math Box: Quadratic Relationships
• Two quantities x and y are said to have a
quadratic relationship if y is proportional to
the square of x.
• y=Ax2, A is a constant
• y ~ x2
• y1 =A(x1)2
y2 =A(x2)2
• y2/y1 =A(x2)2/A(x1)2 = (x2)2/(x1)2 = (x2/x1)2
Falling Objects
• If you drop a rock out of an airplane, the distance d
that it has fallen is proportional to the square of the
time t since you dropped it
• d ~ t2
 d = k ⋅ t2
• If you dropped a rock and it fell 4.9 m in 1 s , how far
would it fall in 3 s ?
• d2/d1 = (t2/t1)2
• d1 = 4.9m
t1 = 1 s
• d2 = x
t2 = 3 s
• Substitute: x/4.9m = (3 s / 1 s)2
•
x/4.9m = (3)2
•
x
=
9 ⋅ 4.9 m = 44.1 m
• Choose the correct velocity-versus-time graph
for a rock that is thrown straight upward, from
the instant it leaves the hand until the instant
it hits the ground.
Grass
• A rough guess is good
enough
• d = 2 inches
• t = once a week
• v = d/t =
2 in / 1week =
• 2in/1wk ⋅ 2.54cm/in ⋅
wk/7day ⋅ day/24 hrs
⋅ 1 hr /3600 sec
• = 8.4 x 10-6 cm/s
• = 8.4 x 10-8 m/s