Elastigirl Saves the Train!
Elastigirl, or Helen Parr, matriarch of the Incredible Family, is an amazing example of many
different concepts we have learned in physics from springs to momentum to drag. Her ability to stretch
her limbs to extreme lengths allows her to propel herself to the tops of buildings, jump from incredible
(pun intended) distances, and even act as her own parachute.
different concepts we have learned in physics from springs to momentum to drag. Her ability to stretch
her limbs to extreme lengths allows her to propel herself to the tops of buildings, jump from incredible
(pun intended) distances, and even act as her own parachute.
The producers did not go easy on Elastigirl, and set her up to have to stop a maglev train which mostly avoids friction by hovering over the tracks due to a system of magnetic forces. In this scene, we see Elastigirl (ingeniously) separate the train in the middle, which appears to break the magnetic aspect of the train and introduce friction. She then stretches her body into a parachute to create enough drag to bring the train to a stop before it falls off the unfinished track. In this problem, we will use the dimensions of the Shanghai Maglev train to calculate how much drag (work of a nonconservative force) Elastigirl produces to save the train and its passengers.
The Shanghai Maglev train can travel up to 431 km/hr. Additionally, the mass of a middle car is
about 20,000 kg and the head is about 30,000 kg. From the video, it looks like Elastigirl separated
the train at one head carriage and one middle carriage, so we will assume the total mass of her
section of the car is 50,000 kg. We’ll also assume the evil villain (The screen Slaver, for those who
haven’t seen the movie) set the track to go its fastest speed if he/she was trying to cause a lot of
destruction. The track of a Maglev train is normally made of steel. The bottom of a Maglev train is
covered in electromagnets which is typically made of copper coiled around another metal. We will
assume the friction occuring between the train and the tracks is between steel and copper, which
has a coefficient of friction of 0.36 (while sliding). We assume the track is clean and dry because this
was the opening day of the train.
about 20,000 kg and the head is about 30,000 kg. From the video, it looks like Elastigirl separated
the train at one head carriage and one middle carriage, so we will assume the total mass of her
section of the car is 50,000 kg. We’ll also assume the evil villain (The screen Slaver, for those who
haven’t seen the movie) set the track to go its fastest speed if he/she was trying to cause a lot of
destruction. The track of a Maglev train is normally made of steel. The bottom of a Maglev train is
covered in electromagnets which is typically made of copper coiled around another metal. We will
assume the friction occuring between the train and the tracks is between steel and copper, which
has a coefficient of friction of 0.36 (while sliding). We assume the track is clean and dry because this
was the opening day of the train.
We will also assume Elastigirl began parachuting at 1 km (1000 meters) from the end of the tracks
where she stops.
where she stops.
Sooo….
Initial velocity= 431 km/hr→ 119.72 m/s
mass: 50,000 kg
μ= .36
d= 1000m
ΔKE= -ΔPE + Wnc
½ m(vf2-vi2)= -μgmd + Welastigirl
½(50,000)(0-119.722)= -(.36)(9.8)(50,000)(1000m) + Welastigirl
-358321960= -176400000 + Welastigirl
-181921960 J= Welastigirl
That’s more than the average US energy consumption for a house in one day!
Go Elastigirl!
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