play phryzby with physics

Dropped From a Truck

solved MotionInAPlane

Q. A truck starts from restvx(start)=0m/s, vy(start)=0m/s and accelerates uniformly at 2.0 m/s²ax(c)=2.0m/s². At t = 10 sΔtc=10s, a stone is dropped by a person standing on the top of the truckay(c)=0m/s² (6 mxy(dropped)=6m high from the ground). Neglect air resistanceax(f)=0m/s², ay(f)=−g, and take g as 10 m/s²g=10m/s². What is the speed of the stone at t = 11 sΔta=11s, in m/s?

y₀v = ?yt carried = 10 st fallingg = 10 m/s²
Inputs
ax
2 m/s²
Δtc
10.00 s
xy
6.00 m
g
10 m/s²
Δta
11.00 s
Outputs
speedv?

How it's solved

Solved with MotionInAPlane

Given

  • ax(c)=2.0m/s²
  • Δtc=10s
  • xy(dropped)=6m
  • g=10m/s²
  • Δta=11s
  • vx(start)=0m/s from “starts from rest”
  • vy(start)=0m/s from “starts from rest”
  • ay(c)=0m/s² from “standing on the top of the truck”
  • ax(f)=0m/s² from “Neglect air resistance”
  • ay(f)=−g from “Neglect air resistance”

Find v(later).

Working
  1. velocity after a time(carried, x)vx(dropped)=vx(start)+ax(c)⋅Δtc
  2. vx(dropped)=0+2⋅10
  3. vx(dropped)=20m/s
  4. time in parts(all along)Δta=Δtc+Δtf
  5. 11=10+Δtf
  6. Δtf=1s
  7. velocity after a time(falling, x)vx(later)=vx(dropped)+ax(f)⋅Δtf
  8. vx(later)=20+0⋅1
  9. vx(later)=20m/s
  10. velocity after a time(carried, y)vy(dropped)=vy(start)+ay(c)⋅Δtc
  11. vy(dropped)=0+0⋅10
  12. vy(dropped)=0m/s
  13. Neglect air resistanceay(f)=−g
  14. ay(f)=−10
  15. ay(f)=−10m/s²
  16. velocity after a time(falling, y)vy(later)=vy(dropped)+ay(f)⋅Δtf
  17. vy(later)=0+(−10)⋅1
  18. vy(later)=−10m/s
  19. magnitude from components(velocity of stone at later from ground)v(later)=vx(later)2+vy(later)2
  20. v(later)=202+(−10)2
  21. v(later)=22.4 m/s
  22. v(later)≈22.4m/sto 3 significant figures
Conclusion

The stone leaves the truck with the truck's velocity and keeps it sideways, since nothing pushes it along any more, while gravity alone speeds it downward.

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 :dropped_from_a_truck do4  kind :numerical5  describes "A truck starts from rest and accelerates uniformly at %{acceleration}. At t = %{dropped_at}, a stone is " \6            "dropped by a person standing on the top of the truck (%{height} high from the ground). Neglect air " \7            "resistance, and take g as %{gravity}. %{speed} at t = %{asked_at}, in m/s?"8  given acceleration: "2.0 m/s2"9  given dropped_at: "10 s"10  given height: "6 m"11  given gravity: "10 m/s2"12  given asked_at: "11 s"13  asks speed: "What is the speed of the stone"14end
solution.rb
1require_relative "../questions/dropped_from_a_truck"2require_relative "../science/motion_in_a_plane/motion_in_a_plane"34solve :dropped_from_a_truck, using: MotionInAPlane do5  objects :stone6  axes :x, :y7  instants :start, :dropped, :later8  stone.goes(:carried, during: start..dropped)9  stone.goes(:falling, during: dropped..later)10  stone.goes(:all_along, during: start..later)1112  take acceleration: stone.acceleration(during: carried, along: x)13  take dropped_at: carried.time_taken14  take height: stone.position(at: dropped, along: y)15  take gravity: g16  take asked_at: all_along.time_taken1718  deduce_from "starts from rest", stone.velocity(at: start, along: x) => "0 m/s", stone.velocity(at: start, along: y) => "0 m/s"19  deduce_from "standing on the top of the truck", stone.acceleration(during: carried, along: y) => "0 m/s2"20  deduce_from "Neglect air resistance", stone.acceleration(during: falling, along: x) => "0 m/s2",21                                        stone.acceleration(during: falling, along: y) => -g2223  speed = stone.speed(at: later)24  answer speed:, in: "m/s", figures: 32526  conclusion "The stone leaves the truck with the truck's velocity and keeps it sideways, since nothing pushes " \27             "it along any more, while gravity alone speeds it downward."28end
playground.rb
1require_relative "../solutions/dropped_from_a_truck"23play_with :dropped_from_a_truck do4  title "Dropped From a Truck"5end
The laws it drew on
quantitywrittenunitswithinfrom
volumevolume——Vectors
massmass——Vectors
speedspeed——Vectors
densitydensity——Vectors
number of molesn——Vectors
angular frequencyangularfrequency——Vectors
workwork——Vectors
currentcurrent——Vectors
temperaturetemperature——Vectors
pressurepressure——Vectors
timets0 … 1e+05Vectors
powerpower——Vectors
total path lengths——Vectors
energyenergy——Vectors
gravitational potentialgravitationalpotential——Vectors
coefficient of frictionμ——Vectors
chargecharge——Vectors
accelerationam/s²—Vectors
velocityvm/s—Vectors
displacementΔxm—Vectors
angular velocityangularvelocity——Vectors
forceforce——Vectors
angular momentumangularmomentum——Vectors
linear momentumplin——Vectors
electric fieldelectricfield——Vectors
average velocityvavm/s—Vectors
magnetic momentmagneticmoment——Vectors
relative velocityvAB——Vectors
impulseimpulse——Vectors
first vectorA—0 … ∞Vectors
second vectorB—0 … ∞Vectors
angle betweenφ—0 … 3.142Vectors
resultantR—0 … ∞Vectors
resultant directionβ—0 … 3.142Vectors
directionα—-3.142 … 3.142Vectors
x componentAx——Vectors
y componentAy——Vectors
positionxm—Velocity
path lengthdm—Velocity
time takenΔts0 … 1e+05Velocity
average speedcavm/s—Velocity
starting positionx0m—Velocity
final positionxm—Velocity
change of velocityΔvm/s—Acceleration
average accelerationaavm/s²—Acceleration
starting velocityv0m/s—Acceleration
final velocityvm/s—Acceleration
gravitygm/s²—UniformAcceleration
displacement of stone during carried along xΔxx(c)m—
position of stone at dropped along xxx(dropped)m—
position of stone at start along xxx(start)m—
displacement of stone during carried along yΔxy(c)m—
position of stone at dropped along yxy(dropped)m—
position of stone at start along yxy(start)m—
displacement of stone during falling along xΔxx(f)m—
position of stone at later along xxx(later)m—
displacement of stone during falling along yΔxy(f)m—
position of stone at later along yxy(later)m—
displacement of stone during all along along xΔxx(a)m—
displacement of stone during all along along yΔxy(a)m—
average velocity of stone during carried along xvav,x(c)m/s—
time taken of carriedΔtcs0 … 1e+05
average velocity of stone during carried along yvav,y(c)m/s—
average velocity of stone during falling along xvav,x(f)m/s—
time taken of fallingΔtfs0 … 1e+05
average velocity of stone during falling along yvav,y(f)m/s—
average velocity of stone during all along along xvav,x(a)m/s—
time taken of all alongΔtas0 … 1e+05
average velocity of stone during all along along yvav,y(a)m/s—
average speed of stone during carriedcav(c)m/s—
path length of stone during carriedd(c)m—
average speed of stone during fallingcav(f)m/s—
path length of stone during fallingd(f)m—
average speed of stone during all alongcav(a)m/s—
path length of stone during all alongd(a)m—
change of velocity of stone during carried along xΔvx(c)m/s—
velocity of stone at dropped from ground along xvx(dropped)m/s—
velocity of stone at start from ground along xvx(start)m/s—
change of velocity of stone during carried along yΔvy(c)m/s—
velocity of stone at dropped from ground along yvy(dropped)m/s—
velocity of stone at start from ground along yvy(start)m/s—
change of velocity of stone during falling along xΔvx(f)m/s—
velocity of stone at later from ground along xvx(later)m/s—
change of velocity of stone during falling along yΔvy(f)m/s—
velocity of stone at later from ground along yvy(later)m/s—
change of velocity of stone during all along along xΔvx(a)m/s—
change of velocity of stone during all along along yΔvy(a)m/s—
average acceleration of stone during carried along xaav,x(c)m/s²—
average acceleration of stone during carried along yaav,y(c)m/s²—
average acceleration of stone during falling along xaav,x(f)m/s²—
average acceleration of stone during falling along yaav,y(f)m/s²—
average acceleration of stone during all along along xaav,x(a)m/s²—
average acceleration of stone during all along along yaav,y(a)m/s²—
acceleration of stone during carried along xax(c)m/s²—
acceleration of stone during carried along yay(c)m/s²—
acceleration of stone during falling along xax(f)m/s²—
acceleration of stone during falling along yay(f)m/s²—
acceleration of stone during all along along xax(a)m/s²—
acceleration of stone during all along along yay(a)m/s²—
acceleration of stone during carrieda(c)m/s²—
acceleration of stone during all alonga(a)m/s²—
acceleration of stone during fallinga(f)m/s²—
velocity of ground at start from ground along xvg,x(start)m/s—
velocity of ground at start from groundvg(start)m/s—
direction of ground at start from groundθg(start)—-3.142 … 3.142
velocity of ground at start from ground along yvg,y(start)m/s—
velocity of ground at dropped from ground along xvg,x(dropped)m/s—
velocity of ground at dropped from groundvg(dropped)m/s—
direction of ground at dropped from groundθg(dropped)—-3.142 … 3.142
velocity of ground at dropped from ground along yvg,y(dropped)m/s—
velocity of ground at later from ground along xvg,x(later)m/s—
velocity of ground at later from groundvg(later)m/s—
direction of ground at later from groundθg(later)—-3.142 … 3.142
velocity of ground at later from ground along yvg,y(later)m/s—
velocity of stone at start from groundv(start)m/s—
direction of stone at start from groundθ(start)—-3.142 … 3.142
velocity of stone at dropped from groundv(dropped)m/s—
direction of stone at dropped from groundθ(dropped)—-3.142 … 3.142
velocity of stone at later from groundv(later)m/s—
direction of stone at later from groundθ(later)—-3.142 … 3.142
displacement of stone during carriedΔx(c)m—
position of stone at droppedx(dropped)m—
position of stone at startx(start)m—
displacement of stone during fallingΔx(f)m—
position of stone at laterx(later)m—
displacement of stone during all alongΔx(a)m—
average velocity of stone during carriedvav(c)m/s—
average velocity of stone during fallingvav(f)m/s—
average velocity of stone during all alongvav(a)m/s—
change of velocity of stone during carriedΔv(c)m/s—
change of velocity of stone during fallingΔv(f)m/s—
change of velocity of stone during all alongΔv(a)m/s—
average acceleration of stone during carriedaav(c)m/s²—
average acceleration of stone during fallingaav(f)m/s²—
average acceleration of stone during all alongaav(a)m/s²—
x0≡xi(start of motion)
starting position
x≡xi(end of motion)
final position
v0≡vi(start of motion)
starting velocity
v≡vi(end of motion)
final velocity
t≡Δtm
time
A=Ax2+Ay2
magnitude from components
di(whole)=di(part 1)+di(part 2)
path in parts
Δtw=Δtp+Δtp
time in parts
ai(part 1)=ai(whole)
steady through its parts
vo,x(t)=vo(t)⋅cos⁡θo(t)
parts of a velocity
R2=A2+B2+2⋅A⋅B⋅cos⁡φ
law of cosines
R⋅sin⁡β=B⋅sin⁡φ
law of sines
R⋅cos⁡β=A+B⋅cos⁡φ
along the first
Ax=A⋅cos⁡α
resolved along x
Ay=A⋅sin⁡α
resolved along y
Δxx(c)=xx(dropped)-xx(start)
change of position(carried, x)
Δxy(c)=xy(dropped)-xy(start)
change of position(carried, y)
Δxx(f)=xx(later)-xx(dropped)
change of position(falling, x)
Δxy(f)=xy(later)-xy(dropped)
change of position(falling, y)
Δxx(a)=xx(later)-xx(start)
change of position(all along, x)
Δxy(a)=xy(later)-xy(start)
change of position(all along, y)
vav,x(c)=Δxx(c)Δtc
displacement a time(carried, x)
vav,y(c)=Δxy(c)Δtc
displacement a time(carried, y)
vav,x(f)=Δxx(f)Δtf
displacement a time(falling, x)
vav,y(f)=Δxy(f)Δtf
displacement a time(falling, y)
vav,x(a)=Δxx(a)Δta
displacement a time(all along, x)
vav,y(a)=Δxy(a)Δta
displacement a time(all along, y)
cav(c)=d(c)Δtc
path a time(carried, x)
cav(c)=d(c)Δtc
path a time(carried, y)
cav(f)=d(f)Δtf
path a time(falling, x)
cav(f)=d(f)Δtf
path a time(falling, y)
cav(a)=d(a)Δta
path a time(all along, x)
cav(a)=d(a)Δta
path a time(all along, y)
Δvx(c)=vx(dropped)-vx(start)
velocity gained(carried, x)
Δvy(c)=vy(dropped)-vy(start)
velocity gained(carried, y)
Δvx(f)=vx(later)-vx(dropped)
velocity gained(falling, x)
Δvy(f)=vy(later)-vy(dropped)
velocity gained(falling, y)
Δvx(a)=vx(later)-vx(start)
velocity gained(all along, x)
Δvy(a)=vy(later)-vy(start)
velocity gained(all along, y)
aav,x(c)=Δvx(c)Δtc
velocity gained a time(carried, x)
aav,y(c)=Δvy(c)Δtc
velocity gained a time(carried, y)
aav,x(f)=Δvx(f)Δtf
velocity gained a time(falling, x)
aav,y(f)=Δvy(f)Δtf
velocity gained a time(falling, y)
aav,x(a)=Δvx(a)Δta
velocity gained a time(all along, x)
aav,y(a)=Δvy(a)Δta
velocity gained a time(all along, y)
vx(dropped)=vx(start)+ax(c)⋅Δtc
velocity after a time(carried, x)
vy(dropped)=vy(start)+ay(c)⋅Δtc
velocity after a time(carried, y)
vx(later)=vx(dropped)+ax(f)⋅Δtf
velocity after a time(falling, x)
vy(later)=vy(dropped)+ay(f)⋅Δtf
velocity after a time(falling, y)
vx(later)=vx(start)+ax(a)⋅Δta
velocity after a time(all along, x)
vy(later)=vy(start)+ay(a)⋅Δta
velocity after a time(all along, y)
xx(dropped)=xx(start)+vx(start)⋅Δtc+ax(c)⋅Δtc22
position after a time(carried, x)
xy(dropped)=xy(start)+vy(start)⋅Δtc+ay(c)⋅Δtc22
position after a time(carried, y)
xx(later)=xx(dropped)+vx(dropped)⋅Δtf+ax(f)⋅Δtf22
position after a time(falling, x)
xy(later)=xy(dropped)+vy(dropped)⋅Δtf+ay(f)⋅Δtf22
position after a time(falling, y)
xx(later)=xx(start)+vx(start)⋅Δta+ax(a)⋅Δta22
position after a time(all along, x)
xy(later)=xy(start)+vy(start)⋅Δta+ay(a)⋅Δta22
position after a time(all along, y)
vx(dropped)2=vx(start)2+2⋅ax(c)⋅(xx(dropped)-xx(start))
velocity after a distance(carried, x)
vy(dropped)2=vy(start)2+2⋅ay(c)⋅(xy(dropped)-xy(start))
velocity after a distance(carried, y)
vx(later)2=vx(dropped)2+2⋅ax(f)⋅(xx(later)-xx(dropped))
velocity after a distance(falling, x)
vy(later)2=vy(dropped)2+2⋅ay(f)⋅(xy(later)-xy(dropped))
velocity after a distance(falling, y)
vx(later)2=vx(start)2+2⋅ax(a)⋅(xx(later)-xx(start))
velocity after a distance(all along, x)
vy(later)2=vy(start)2+2⋅ay(a)⋅(xy(later)-xy(start))
velocity after a distance(all along, y)
xx(dropped)-xx(start)=(vx(dropped)+vx(start))⋅Δtc2
mean of the velocities(carried, x)
xy(dropped)-xy(start)=(vy(dropped)+vy(start))⋅Δtc2
mean of the velocities(carried, y)
xx(later)-xx(dropped)=(vx(later)+vx(dropped))⋅Δtf2
mean of the velocities(falling, x)
xy(later)-xy(dropped)=(vy(later)+vy(dropped))⋅Δtf2
mean of the velocities(falling, y)
xx(later)-xx(start)=(vx(later)+vx(start))⋅Δta2
mean of the velocities(all along, x)
xy(later)-xy(start)=(vy(later)+vy(start))⋅Δta2
mean of the velocities(all along, y)
d(a)=d(c)+d(f)
path in parts(all along)
Δta=Δtc+Δtf
time in parts(all along)
a(c)=a(a)
steady through its parts(all along, 1)
a(f)=a(a)
steady through its parts(all along, 2)
vg,x(start)=vg(start)⋅cos⁡θg(start)
parts of a velocity(ground, start, x)
vg,y(start)=vg(start)⋅sin⁡θg(start)
parts of a velocity(ground, start, y)
vg,x(dropped)=vg(dropped)⋅cos⁡θg(dropped)
parts of a velocity(ground, dropped, x)
vg,y(dropped)=vg(dropped)⋅sin⁡θg(dropped)
parts of a velocity(ground, dropped, y)
vg,x(later)=vg(later)⋅cos⁡θg(later)
parts of a velocity(ground, later, x)
vg,y(later)=vg(later)⋅sin⁡θg(later)
parts of a velocity(ground, later, y)
vx(start)=v(start)⋅cos⁡θ(start)
parts of a velocity(stone, start, x)
vy(start)=v(start)⋅sin⁡θ(start)
parts of a velocity(stone, start, y)
vx(dropped)=v(dropped)⋅cos⁡θ(dropped)
parts of a velocity(stone, dropped, x)
vy(dropped)=v(dropped)⋅sin⁡θ(dropped)
parts of a velocity(stone, dropped, y)
vx(later)=v(later)⋅cos⁡θ(later)
parts of a velocity(stone, later, x)
vy(later)=v(later)⋅sin⁡θ(later)
parts of a velocity(stone, later, y)
Δx(c)=Δxx(c)2+Δxy(c)2
magnitude from components(displacement of stone during carried)
x(dropped)=xx(dropped)2+xy(dropped)2
magnitude from components(position of stone at dropped)
x(start)=xx(start)2+xy(start)2
magnitude from components(position of stone at start)
Δx(f)=Δxx(f)2+Δxy(f)2
magnitude from components(displacement of stone during falling)
x(later)=xx(later)2+xy(later)2
magnitude from components(position of stone at later)
Δx(a)=Δxx(a)2+Δxy(a)2
magnitude from components(displacement of stone during all along)
vav(c)=vav,x(c)2+vav,y(c)2
magnitude from components(average velocity of stone during carried)
vav(f)=vav,x(f)2+vav,y(f)2
magnitude from components(average velocity of stone during falling)
vav(a)=vav,x(a)2+vav,y(a)2
magnitude from components(average velocity of stone during all along)
Δv(c)=Δvx(c)2+Δvy(c)2
magnitude from components(change of velocity of stone during carried)
v(dropped)=vx(dropped)2+vy(dropped)2
magnitude from components(velocity of stone at dropped from ground)
v(start)=vx(start)2+vy(start)2
magnitude from components(velocity of stone at start from ground)
Δv(f)=Δvx(f)2+Δvy(f)2
magnitude from components(change of velocity of stone during falling)
v(later)=vx(later)2+vy(later)2
magnitude from components(velocity of stone at later from ground)
Δv(a)=Δvx(a)2+Δvy(a)2
magnitude from components(change of velocity of stone during all along)
aav(c)=aav,x(c)2+aav,y(c)2
magnitude from components(average acceleration of stone during carried)
aav(f)=aav,x(f)2+aav,y(f)2
magnitude from components(average acceleration of stone during falling)
aav(a)=aav,x(a)2+aav,y(a)2
magnitude from components(average acceleration of stone during all along)
a(c)=ax(c)2+ay(c)2
magnitude from components(acceleration of stone during carried)
a(f)=ax(f)2+ay(f)2
magnitude from components(acceleration of stone during falling)
a(a)=ax(a)2+ay(a)2
magnitude from components(acceleration of stone during all along)
vg(start)=vg,x(start)2+vg,y(start)2
magnitude from components(velocity of ground at start from ground)
vg(dropped)=vg,x(dropped)2+vg,y(dropped)2
magnitude from components(velocity of ground at dropped from ground)
vg(later)=vg,x(later)2+vg,y(later)2
magnitude from components(velocity of ground at later from ground)
ay(f)=−g
Neglect air resistance