A throw on the Moon

solved Projectile

Q. A ball is thrown at 20 m/s $v_{0} = 20$ m/s, 45° $θ_{0} = 45 °$ above the ground, on the Moon $g = 1.62$ m/s². How far away does it land $x_{1,y} = 0$ m, in metres?

Inputs

speed

v_{0}

20.0 m/s

angle

θ_{0}

45.00°

Outputs

distance

x_{1,x}

How it's solved

Solved with Projectile

Given

$v_{0} = 20$ m/s
$θ_{0} = 45 °$
$g = 1.62$ m/s² from “on the Moon”
$x_{1,y} = 0$ m from “land”

Assumed

$x_{0,x} = 0$ m
$x_{0,y} = 0$ m

Find $x_{1,x}$ .

Working

parts of a velocity(ball, start of flying, y) $v_{0,y} = v_{0} \cdot \sin θ_{0}$
$v_{0,y} = 20 \cdot \sin 45 °$
$v_{0,y} = 14.1421356$ m/s
falling freely(flying, y) $a_{y} = - g$
$a_{y} = - 1.62$
$a_{y} = −1.62$ m/s²
position after a time(flying, y) $x_{1,y} = x_{0,y} + v_{0,y} \cdot Δ t + \frac{a_{y} \cdot {Δ t}^{2}}{2}$
$0 = 0 + 14.1421356 \cdot Δ t + \frac{(−1.62) \cdot {Δ t}^{2}}{2}$
$Δ t = 0, 17.4594267$ sthe start is set aside, as a later time fits
$Δ t = 17.4594267$ s
parts of a velocity(ball, start of flying, x) $v_{0,x} = v_{0} \cdot \cos θ_{0}$
$v_{0,x} = 20 \cdot \cos 45 °$
$v_{0,x} = 14.1421356$ m/s
falling freely(flying, x) $a_{x} = 0$
$a_{x} = 0$ m/s²
position after a time(flying, x) $x_{1,x} = x_{0,x} + v_{0,x} \cdot Δ t + \frac{a_{x} \cdot {Δ t}^{2}}{2}$
$x_{1,x} = 0 + 14.1421356 \cdot 17.4594267 + \frac{0 \cdot {17.4594267}^{2}}{2}$
$x_{1,x} = 246.91 m$

Conclusion

The range goes as one over the pull, so where gravity is weaker the same throw carries further in the same proportion.

The web of concepts

given read from the words equation asked

The Ruby that solves it

The question and its solution are small Ruby files. The engine runs them.

question.rb

1require_relative "../physics"23question :throw_on_the_moon do4  kind :numerical5  describes "A ball is thrown at %{speed}, %{angle} above the ground, on the Moon. %{distance}, in metres?"6  given speed: "20 m/s"7  given angle: "45 deg"8  asks distance: "How far away does it land"9end

solution.rb

1require_relative "../questions/throw_on_the_moon"2require_relative "../science/motion_in_a_plane/projectile"3require_relative "../science/motion_in_a_plane/gravity"45solve :throw_on_the_moon, using: Projectile do6  objects :ball7  axes :x, :y8  ball.goes(:flying)9  take speed: ball.initial_speed, angle: ball.initial_direction10  deduce_from "on the Moon", g => GRAVITY.fetch("moon")11  assume ball.initial_position(along: x) => "0 m", ball.initial_position(along: y) => "0 m"12  deduce_from "land", ball.final_position(along: y) => "0 m"13  distance = ball.final_position(along: x)14  answer distance:, in: "m"15  conclusion "The range goes as one over the pull, so where gravity is weaker the same throw " \16             "carries further in the same proportion."17end

playground.rb

1require_relative "../solutions/throw_on_the_moon"23play_with :throw_on_the_moon do4  title "A throw on the Moon"5end

The laws it drew on

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 ball during flying along x	$Δ x_{x}$	m	—
position of ball at end of flying along x	$x_{1,x}$	m	—
position of ball at start of flying along x	$x_{0,x}$	m	—
displacement of ball during flying along y	$Δ x_{y}$	m	—
position of ball at end of flying along y	$x_{1,y}$	m	—
position of ball at start of flying along y	$x_{0,y}$	m	—
average velocity of ball during flying along x	$v_{av,x}$	m/s	—
time taken of flying	$Δ t$	s	0 … 1e+05
average velocity of ball during flying along y	$v_{av,y}$	m/s	—
average speed of ball during flying	$c_{av}$	m/s	—
path length of ball during flying	$d$	m	—
change of velocity of ball during flying along x	$Δ v_{x}$	m/s	—
velocity of ball at end of flying from ground along x	$v_{1,x}$	m/s	—
velocity of ball at start of flying from ground along x	$v_{0,x}$	m/s	—
change of velocity of ball during flying along y	$Δ v_{y}$	m/s	—
velocity of ball at end of flying from ground along y	$v_{1,y}$	m/s	—
velocity of ball at start of flying from ground along y	$v_{0,y}$	m/s	—
average acceleration of ball during flying along x	$a_{av,x}$	m/s²	—
average acceleration of ball during flying along y	$a_{av,y}$	m/s²	—
acceleration of ball during flying along x	$a_{x}$	m/s²	—
acceleration of ball 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 ball at start of flying from ground	$v_{0}$	m/s	—
direction of ball at start of flying from ground	$θ_{0}$	—	-3.142 … 3.142
velocity of ball at end of flying from ground	$v_{1}$	m/s	—
direction of ball at end of flying from ground	$θ_{1}$	—	-3.142 … 3.142
displacement of ball during flying	$Δ x$	m	—
position of ball at end of flying	$x_{1}$	m	—
position of ball at start of flying	$x_{0}$	m	—
average velocity of ball during flying	$v_{av}$	m/s	—
change of velocity of ball during flying	$Δ v$	m/s	—
average acceleration of ball during flying	$a_{av}$	m/s²	—
acceleration of ball 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(ball, start of flying, x)

v_{0,y} = v_{0} \cdot \sin θ_{0}

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

v_{1,x} = v_{1} \cdot \cos θ_{1}

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

v_{1,y} = v_{1} \cdot \sin θ_{1}

parts of a velocity(ball, 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 ball during flying)

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

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

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

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

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

magnitude from components(average velocity of ball during flying)

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

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

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

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

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

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

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

magnitude from components(average acceleration of ball during flying)

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

magnitude from components(acceleration of ball 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)