Chen Zhuo’s gaze slowly turned to the first problem.
The problem was short, just two lines of text.
[Problem: A rocket with mass M is launched vertically in a medium with a drag coefficient of k.
Assuming the fuel ejection velocity u is constant relative to the rocket, and the rocket’s mass decreases linearly with time t... Find the mass ratio when the rocket reaches its maximum velocity.]
This was a variable-mass problem.
In other words, a twisted version of the legendary Tsiolkovsky rocket equation.
In ordinary middle school physics, mass (m) is always a constant.
But this problem tossed that constant ’m’ right out the window from the get-go.
It became a variable—a function, m, that continuously decreased over time.
This meant that Newton’s second law, F=ma, was invalid here.
One had to use the differential form of the momentum theorem: F=dp/dt.
Chen Zhuo pushed up his glasses.
’So this is what Old Zhou meant by ’insane’?’
’It really is insane, especially for a problem in a middle school physics workbook.’
But Chen Zhuo was happy.
Genuinely happy. It was the involuntary, radiating joy of a mind about to absorb new knowledge and tear into a new problem.
Chen Zhuo picked up his mechanical pencil and wrote the first formula in his notebook.
There was no hurried scratching.
He wrote very slowly.
Every stroke seemed as if it were being carved into the paper.
Five minutes of thought, thirty seconds of writing.
His brain began to enter that familiar high-load state.
The air around him seemed to grow thick and viscous.
The hum of the air conditioner vanished.
The rustling of Old Zhou’s newspaper vanished.
The sound of Li Hao flipping through his test paper also vanished.
In his world, all that remained was the lonely rocket ascending through a resistive medium, and the Greek letters that represented truth.
He constructed a coordinate system in his mind.
The rocket was no longer just words on a page; it had become a silvery-white metal cylinder, its tail spewing brilliant flames.
The fuel was decreasing, the mass was decreasing, the velocity was increasing, and the drag was also increasing non-linearly.
It was a dynamic interplay of forces.
Differential equations.
Chen Zhuo wrote line after line of equations on the paper.
This was the true face of the physical world.
Chaotic, non-linear, and filled with uncertainty.
The pencil tip glided across the paper.
He didn’t need a computer.
Those complex integrals flowed through his mind as naturally as a stream.
Old Zhou sat at the teacher’s desk. He had switched to the evening paper from two days ago, sipping his tea as he read.
Occasionally, he would lift his head and glance over the classroom from above the rim of his reading glasses.
The two in the front row were drenched in sweat—a normal sight.
The one in the back, perfectly still—a pleasant surprise.
An imperceptible smile touched the corner of Old Zhou’s mouth before he lowered his head and returned to his newspaper.
「4:00 PM.」
An hour and a half went by.
The battle in the front row seemed to have reached a fever pitch, but also a bottleneck.
Li Hao was stuck.
It was a classic rigid body rotation problem from a physics competition, involving the moment of inertia and a non-inertial frame of reference.
The problem presented a rotating disk with a slider on it, and asked for an analysis of the slider’s trajectory under the effect of the Coriolis force.
Li Hao had already drawn five free-body diagrams and written out three equations on his scratch paper.
But he couldn’t solve it.
The differential equation was too complex. His mathematical toolbox, stocked only with middle school and a little bit of high school knowledge, was completely unable to untie such a knot.
"HSSS..."
Li Hao sucked in a sharp breath and slammed his pen down on the desk in frustration.
Sweat trickled down his temples, dripping onto the test paper and smudging a patch of ink.
He felt like his brain had turned to mush, and a sense of defeat slowly began to consume him from within.
He glanced at Zhang Wei beside him.
Zhang Wei had given up long ago. He was slumped over his desk, using a compass to poke holes in an eraser, clearly having entered a state of sage-like detachment.
Li Hao refused to accept it.
He was first in his grade, the one who was supposed to take first place in the provincial competition.
He gritted his teeth, picked up his test paper, and decided to go to the teacher’s desk to ask Old Zhou.
Even getting a scolding was better than just sitting here wasting time.
He stood up and walked to the front of the teacher’s desk.
Old Zhou was refilling his tea mug.
"Teacher, this problem..."
Li Hao pointed at the paper, his voice a little hoarse.
Old Zhou glanced at it.
"A non-inertial frame?" Old Zhou said casually. "This problem is beyond the curriculum. Use conservation of energy to solve it. Don’t analyze the forces; you’ll just tie yourself in knots."
"Conservation of energy?"
Li Hao froze for a moment.
"Rotational kinetic energy plus potential energy. Then subtract the work done by friction," Old Zhou offered a hint. "Go back and try calculating it again."
Li Hao nodded, only half-understanding.
He walked back, paper in hand.
As if guided by some unseen force, his steps slowed as he passed the back of the lab.
The nine-year-old kid in the corner was still sitting there.
His posture had barely changed.
His left hand cupped his chin, his right hand twirled a pencil.
The tattered red book lay open.
But he wasn’t writing.
He was just staring into space.
Li Hao was a little curious, and a little indignant.
’Why is it that we’re here working ourselves to death, while you just get to sit there and stare into space?’
’Didn’t Old Zhou say this book was supposed to be hard?’
Chen Zhuo seemed completely unaware of Li Hao’s approach, his gaze still fixed blankly on a certain page in the book.
Li Hao took the opportunity to sneak a peek.
Just one glance.
And Li Hao’s feet froze in place.
He saw the contents of the page.
It wasn’t a problem written in the familiar Chinese characters.
It was a pile of letters that looked like tadpoles, with barbs and circles.
He recognized the script.
Russian.
But that wasn’t the most terrifying part.

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