Off a Cliff — phryzby

Q. A hiker at the edge of a cliff 490 m high throws a stone horizontally at 15 m/s. Taking g as 9.8 m/s², how long does it take to reach the ground, in seconds? expects 10.00 s

What the draft establishes

Fills in once a draft is checked.

The web of concepts

given read from the words equation asked

The equations it used

None yet.

Check an answer

Q. A hiker at the edge of a cliff 490 m high $x_{0,y} = 490$ m throws a stone horizontally $v_{0,y} = 0$ m/s at 15 m/s $v_{0,x} = 15$ m/s. Taking g as 9.8 m/s² $g = 9.8$ m/s², how long does it take to reach the ground $x_{1,y} = 0$ m, in seconds?

The playground

Inputs

speed

v_{0,x}

15.0 m/s

gravity

g

9.8 m/s²

Outputs

time

Δ t

The solution

Solved with Projectile

Given

$v_{0,x} = 15$ m/s
$g = 9.8$ m/s²
$v_{0,y} = 0$ m/s from “horizontally”
$x_{0,y} = 490$ m from “490 m high”
$x_{1,y} = 0$ m from “reach the ground”

Find $Δ t$ .

Working

falling freely(flying, y) $a_{y} = - g$
$a_{y} = - 9.8$
$a_{y} = −9.8$ m/s²
position after a time(flying, y) $x_{1,y} = x_{0,y} + v_{0,y} \cdot Δ t + \frac{a_{y} \cdot {Δ t}^{2}}{2}$
$0 = 490 + 0 \cdot Δ t + \frac{(−9.8) \cdot {Δ t}^{2}}{2}$
$Δ t = 10.00 s$

Conclusion

Thrown sideways, the stone starts with no upward speed, so it falls exactly as long as a stone dropped from the same height would. The sideways speed changes where it lands, not when.

The Ruby

1require_relative "../physics"23question :off_a_cliff do4  kind :numerical5  describes "A hiker at the edge of a cliff 490 m high throws a stone horizontally at %{speed}. Taking g " \6          "as %{gravity}, %{time}, in seconds?"7  given speed: "15 m/s"8  given gravity: "9.8 m/s2"9  asks time: "how long does it take to reach the ground"10end

1require_relative "../questions/off_a_cliff"2require_relative "../science/motion_in_a_plane/projectile"34solve :off_a_cliff, using: Projectile do5  objects :stone6  axes :x, :y7  stone.goes(:flying)8  take speed: stone.initial_velocity(along: x), gravity: g9  deduce_from "horizontally", stone.initial_velocity(along: y) => "0 m/s"10  deduce_from "490 m high", stone.initial_position(along: y) => "490 m"11  deduce_from "reach the ground", stone.final_position(along: y) => "0 m"12  time = flying.time_taken13  answer time:, in: "s"14  conclusion "Thrown sideways, the stone starts with no upward speed, so it falls exactly as long " \15             "as a stone dropped from the same height would. The sideways speed changes where it " \16             "lands, not when."17end

1require_relative "../solutions/off_a_cliff"23play_with :off_a_cliff do4  title "Off a Cliff"5end

The laws

quantity	written	units	within	from
volume	$volume$	—	—	Vectors
mass	$mass$	—	—	Vectors
speed	$speed$	—	—	Vectors
density	$density$	—	—	Vectors
number of moles	$n$	—	—	Vectors
angular frequency	${angular}_{frequency}$	—	—	Vectors
work	$work$	—	—	Vectors
current	$current$	—	—	Vectors
temperature	$temperature$	—	—	Vectors
pressure	$pressure$	—	—	Vectors
time	$t$	s	0 … 1e+05	Vectors
power	$power$	—	—	Vectors
total path length	$s$	—	—	Vectors
energy	$energy$	—	—	Vectors
gravitational potential	${gravitational}_{potential}$	—	—	Vectors
coefficient of friction	$μ$	—	—	Vectors
charge	$charge$	—	—	Vectors
acceleration	$a$	m/s²	—	Vectors
velocity	$v$	m/s	—	Vectors
displacement	$Δ x$	m	—	Vectors
angular velocity	${angular}_{velocity}$	—	—	Vectors
force	$force$	—	—	Vectors
angular momentum	${angular}_{momentum}$	—	—	Vectors
linear momentum	$p_{lin}$	—	—	Vectors
electric field	${electric}_{field}$	—	—	Vectors
average velocity	$v_{av}$	m/s	—	Vectors
magnetic moment	${magnetic}_{moment}$	—	—	Vectors
relative velocity	$v_{AB}$	—	—	Vectors
impulse	$impulse$	—	—	Vectors
first vector	$A$	—	0 … ∞	Vectors
second vector	$B$	—	0 … ∞	Vectors
angle between	$φ$	—	0 … 3.142	Vectors
resultant	$R$	—	0 … ∞	Vectors
resultant direction	$β$	—	0 … 3.142	Vectors
direction	$α$	—	-3.142 … 3.142	Vectors
x component	$A_{x}$	—	—	Vectors
y component	$A_{y}$	—	—	Vectors
position	$x$	m	—	Velocity
path length	$d$	m	—	Velocity
time taken	$Δ t$	s	0 … 1e+05	Velocity
average speed	$c_{av}$	m/s	—	Velocity
starting position	$x_{0}$	m	—	Velocity
final position	$x$	m	—	Velocity
change of velocity	$Δ v$	m/s	—	Acceleration
average acceleration	$a_{av}$	m/s²	—	Acceleration
starting velocity	$v_{0}$	m/s	—	Acceleration
final velocity	$v$	m/s	—	Acceleration
gravity	$g$	m/s²	—	UniformAcceleration
displacement of stone during flying along x	$Δ x_{x}$	m	—
position of stone at end of flying along x	$x_{1,x}$	m	—
position of stone at start of flying along x	$x_{0,x}$	m	—
displacement of stone during flying along y	$Δ x_{y}$	m	—
position of stone at end of flying along y	$x_{1,y}$	m	—
position of stone at start of flying along y	$x_{0,y}$	m	—
average velocity of stone during flying along x	$v_{av,x}$	m/s	—
time taken of flying	$Δ t$	s	0 … 1e+05
average velocity of stone during flying along y	$v_{av,y}$	m/s	—
average speed of stone during flying	$c_{av}$	m/s	—
path length of stone during flying	$d$	m	—
change of velocity of stone during flying along x	$Δ v_{x}$	m/s	—
velocity of stone at end of flying from ground along x	$v_{1,x}$	m/s	—
velocity of stone at start of flying from ground along x	$v_{0,x}$	m/s	—
change of velocity of stone during flying along y	$Δ v_{y}$	m/s	—
velocity of stone at end of flying from ground along y	$v_{1,y}$	m/s	—
velocity of stone at start of flying from ground along y	$v_{0,y}$	m/s	—
average acceleration of stone during flying along x	$a_{av,x}$	m/s²	—
average acceleration of stone during flying along y	$a_{av,y}$	m/s²	—
acceleration of stone during flying along x	$a_{x}$	m/s²	—
acceleration of stone during flying along y	$a_{y}$	m/s²	—
velocity of ground at start of flying from ground along x	$v_{0,g,x}$	m/s	—
velocity of ground at start of flying from ground	$v_{0,g}$	m/s	—
direction of ground at start of flying from ground	$θ_{0,g}$	—	-3.142 … 3.142
velocity of ground at start of flying from ground along y	$v_{0,g,y}$	m/s	—
velocity of ground at end of flying from ground along x	$v_{1,g,x}$	m/s	—
velocity of ground at end of flying from ground	$v_{1,g}$	m/s	—
direction of ground at end of flying from ground	$θ_{1,g}$	—	-3.142 … 3.142
velocity of ground at end of flying from ground along y	$v_{1,g,y}$	m/s	—
velocity of stone at start of flying from ground	$v_{0}$	m/s	—
direction of stone at start of flying from ground	$θ_{0}$	—	-3.142 … 3.142
velocity of stone at end of flying from ground	$v_{1}$	m/s	—
direction of stone at end of flying from ground	$θ_{1}$	—	-3.142 … 3.142
displacement of stone during flying	$Δ x$	m	—
position of stone at end of flying	$x_{1}$	m	—
position of stone at start of flying	$x_{0}$	m	—
average velocity of stone during flying	$v_{av}$	m/s	—
change of velocity of stone during flying	$Δ v$	m/s	—
average acceleration of stone during flying	$a_{av}$	m/s²	—
acceleration of stone during flying	$a$	m/s²	—

x_{0} \equiv x_{i} (start of motion)

starting position

x \equiv x_{i} (end of motion)

final position

v_{0} \equiv v_{i} (start of motion)

starting velocity

v \equiv v_{i} (end of motion)

final velocity

t \equiv Δ t_{m}

time

A = \sqrt{{A_{x}}^{2} + {A_{y}}^{2}}

magnitude from components

d_{i} (whole) = d_{i} (part 1) + d_{i} (part 2)

path in parts

Δ t_{w} = Δ t_{p} + Δ t_{p}

time in parts

a_{i} (part 1) = a_{i} (whole)

steady through its parts

v_{o,x} (t) = v_{o} (t) \cdot \cos θ_{o} (t)

parts of a velocity

a_{i,x} (m) = 0

falling freely

R^{2} = A^{2} + B^{2} + 2 \cdot A \cdot B \cdot \cos φ

law of cosines

R \cdot \sin β = B \cdot \sin φ

law of sines

R \cdot \cos β = A + B \cdot \cos φ

along the first

A_{x} = A \cdot \cos α

resolved along x

A_{y} = A \cdot \sin α

resolved along y

Δ x_{x} = x_{1,x} - x_{0,x}

change of position(flying, x)

Δ x_{y} = x_{1,y} - x_{0,y}

change of position(flying, y)

v_{av,x} = \frac{Δ x_{x}}{Δ t}

displacement a time(flying, x)

v_{av,y} = \frac{Δ x_{y}}{Δ t}

displacement a time(flying, y)

c_{av} = \frac{d}{Δ t}

path a time(flying, x)

c_{av} = \frac{d}{Δ t}

path a time(flying, y)

Δ v_{x} = v_{1,x} - v_{0,x}

velocity gained(flying, x)

Δ v_{y} = v_{1,y} - v_{0,y}

velocity gained(flying, y)

a_{av,x} = \frac{Δ v_{x}}{Δ t}

velocity gained a time(flying, x)

a_{av,y} = \frac{Δ v_{y}}{Δ t}

velocity gained a time(flying, y)

v_{1,x} = v_{0,x} + a_{x} \cdot Δ t

velocity after a time(flying, x)

v_{1,y} = v_{0,y} + a_{y} \cdot Δ t

velocity after a time(flying, y)

x_{1,x} = x_{0,x} + v_{0,x} \cdot Δ t + \frac{a_{x} \cdot {Δ t}^{2}}{2}

position after a time(flying, x)

x_{1,y} = x_{0,y} + v_{0,y} \cdot Δ t + \frac{a_{y} \cdot {Δ t}^{2}}{2}

position after a time(flying, y)

{v_{1,x}}^{2} = {v_{0,x}}^{2} + 2 \cdot a_{x} \cdot (x_{1,x} - x_{0,x})

velocity after a distance(flying, x)

{v_{1,y}}^{2} = {v_{0,y}}^{2} + 2 \cdot a_{y} \cdot (x_{1,y} - x_{0,y})

velocity after a distance(flying, y)

x_{1,x} - x_{0,x} = \frac{(v_{1,x} + v_{0,x}) \cdot Δ t}{2}

mean of the velocities(flying, x)

x_{1,y} - x_{0,y} = \frac{(v_{1,y} + v_{0,y}) \cdot Δ t}{2}

mean of the velocities(flying, y)

v_{0,g,x} = v_{0,g} \cdot \cos θ_{0,g}

parts of a velocity(ground, start of flying, x)

v_{0,g,y} = v_{0,g} \cdot \sin θ_{0,g}

parts of a velocity(ground, start of flying, y)

v_{1,g,x} = v_{1,g} \cdot \cos θ_{1,g}

parts of a velocity(ground, end of flying, x)

v_{1,g,y} = v_{1,g} \cdot \sin θ_{1,g}

parts of a velocity(ground, end of flying, y)

v_{0,x} = v_{0} \cdot \cos θ_{0}

parts of a velocity(stone, start of flying, x)

v_{0,y} = v_{0} \cdot \sin θ_{0}

parts of a velocity(stone, start of flying, y)

v_{1,x} = v_{1} \cdot \cos θ_{1}

parts of a velocity(stone, end of flying, x)

v_{1,y} = v_{1} \cdot \sin θ_{1}

parts of a velocity(stone, end of flying, y)

a_{x} = 0

falling freely(flying, x)

a_{y} = - g

falling freely(flying, y)

Δ x = \sqrt{{Δ x_{x}}^{2} + {Δ x_{y}}^{2}}

magnitude from components(displacement of stone during flying)

x_{1} = \sqrt{{x_{1,x}}^{2} + {x_{1,y}}^{2}}

magnitude from components(position of stone at end of flying)

x_{0} = \sqrt{{x_{0,x}}^{2} + {x_{0,y}}^{2}}

magnitude from components(position of stone at start of flying)

v_{av} = \sqrt{{v_{av,x}}^{2} + {v_{av,y}}^{2}}

magnitude from components(average velocity of stone during flying)

Δ v = \sqrt{{Δ v_{x}}^{2} + {Δ v_{y}}^{2}}

magnitude from components(change of velocity of stone during flying)

v_{1} = \sqrt{{v_{1,x}}^{2} + {v_{1,y}}^{2}}

magnitude from components(velocity of stone at end of flying from ground)

v_{0} = \sqrt{{v_{0,x}}^{2} + {v_{0,y}}^{2}}

magnitude from components(velocity of stone at start of flying from ground)

a_{av} = \sqrt{{a_{av,x}}^{2} + {a_{av,y}}^{2}}

magnitude from components(average acceleration of stone during flying)

a = \sqrt{{a_{x}}^{2} + {a_{y}}^{2}}

magnitude from components(acceleration of stone during flying)

v_{0,g} = \sqrt{{v_{0,g,x}}^{2} + {v_{0,g,y}}^{2}}

magnitude from components(velocity of ground at start of flying from ground)

v_{1,g} = \sqrt{{v_{1,g,x}}^{2} + {v_{1,g,y}}^{2}}

magnitude from components(velocity of ground at end of flying from ground)