AP Physics – Homework Oh the Homework – 4 ans
1. A can of tuna is dropped from a building. If the can takes 3.2 seconds to strike the ground, what distance did it
fall?
x=
m⎞
1 2 1⎛
2
at = ⎜ 9.8 2 ⎟ ( 3.2 s ) =
s ⎠
2
2⎝
50. m
2. An engine falls off of a 737 from a height of 2500 m. Ignoring wind resistance, how fast is the thing traveling
when it smacks into the turf?
v 2 = v0 + 2ax
v = 2ax
2
m⎞
⎛
= 2 ⎜ 9.8 2 ⎟ ( 2500 m )
s ⎠
⎝
=
220
m
s
3. A ball is thrown straight down from a bridge with an initial velocity of 18.5 m/s. If it travels for 2.3 sec, how high
is the bridge?
x=
1 2
at + vi t
2
1⎛
m⎞
m
2
= ⎜ 9.8 2 ⎟ ( 2.3 s ) + 18.5 ( 2.3 s ) =
2⎝
s
s ⎠
68 m
4. A ball, initially at rest, rolls down a ramp. It experiences an acceleration of 1.2 m/s2. If it rolls a distance of 1.8
m, how fast is it traveling?
v = 2ax
v 2 = v0 + 2ax
2
m⎞
⎛
= 2 ⎜1.2 2 ⎟ (1.8 m )
⎝ s ⎠
=
2.1 m
5. A ball is thrown straight up. If its initial velocity is 24 m/s, how high does it rise before it begins falling down?
v 2 = v0 + 2ax
x=
2
6.
−v0
2a
2
⎛
⎛ m ⎞ ⎛ 1 ⎞⎜ 1
= − ⎜ 24 ⎟ ⎜ ⎟ ⎜
s ⎠ ⎝ 2 ⎠ ⎜ −9.8 m
⎝
⎜
s2
⎝
2
⎞
⎟
⎟ =
⎟⎟
⎠
29 m
A ball is thrown straight up, it rises 12.5 m before it falls back down. What was its initial speed?
v 2 = v0 + 2ax
v0 = 2ax
2
m⎞
⎛
= − 2 ⎜ 9.8 2 ⎟ (12.5 m )
s ⎠
⎝
=
15.7
m
s
7. A ball is thrown straight down from a bridge with an initial velocity of 18.5 m/s. The bridge is 22.0 m above the
river. How much time to hit the water?
2
m⎞
m⎞
m
⎛
⎛
2
v = v0 + 2ax = ⎜18.5 ⎟ + 2 ⎜ 9.8 2 ⎟ ( 22.0 m ) = 27.8
s⎠
s ⎠
s
⎝
⎝
⎛
⎞
v − v0 ⎛
m
m ⎞⎜ 1 ⎟
Or
= ⎜ 27.8 − 18.5 ⎟ ⎜
t=
0.949 s
⎟=
a
s
s ⎠ ⎜ 9.8 m ⎟
⎝
⎜
⎟
s2 ⎠
⎝
v 2 = v0 + 2ax
2
v = v0 + at
1
x = vot + at 2
2
t=
−vo ±
1 2
at + vot − x = 0
2
( vo )2 − 4 ⎜⎛
2
−b ± b 2 − 4ac
x=
2a
m⎞
m⎞
m⎞
⎛
⎛
⎛ 1 ⎞⎛
− ⎜18.5 ⎟ ± ⎜18.5 ⎟ − 4 ⎜ ⎟ ⎜ 9.8 2 ⎟ ( −22.0 m )
s⎠
s⎠
⎝
⎝
⎝ 2 ⎠⎝
s ⎠
=
m
1
⎞
⎛ ⎞⎛
2 ⎜ ⎟⎜ 9.8 2 ⎟
2
⎝ ⎠⎝
s ⎠
m⎞
m
⎛
m
− ⎜18.5 ⎟ + 27.81
9.31
s⎠
s
s
= ⎝
=
=
0.950 s
m
m
⎛
⎞
⎛
⎞
⎜ 9.8 2 ⎟
⎜ 9.8 2 ⎟
s ⎠
s ⎠
⎝
⎝
1 ⎞
a⎟x
⎝2 ⎠
⎛1 ⎞
2⎜ a ⎟
⎝2 ⎠
m⎞
m
⎛
− ⎜18.5 ⎟ ± 27.81
s⎠
s
t= ⎝
m
⎛
⎞
⎜ 9.8 2 ⎟
s ⎠
⎝
quadratic equation so: ax 2 + bx + c = 0