Twenty minutes or less.

This week is a practical week. Laboratory 1 runs in the lab class (spring constant, coefficient of kinetic friction, ramp displacement, with a worksheet submission), and Portfolio 5/6 is completed in the workshop class. Plan accordingly — you need both the theory and the lab procedure ready.

5-minute version

Three concepts, one sentence each:

• Work — energy crossing the system boundary: $W=|F|\cos \theta \cdot |s|$ for constant force, area under $F$ vs $s$ for variable force.
• Energy stores — $KE=\frac{1}{2}m{v}^2$, $P{E}_g=mgh$, $P{E}_{\text{spring}}=\frac{1}{2}k{x}^2$.
• Balance — $K{E}_i+P{E}_i+W_{\text{on}}=K{E}_f+P{E}_f+W_{\text{by}}$. Friction is always a $W_{\text{by}}$ term.

Open the cheatsheet quiz, do 3 easy questions, close it. You’re prepped — now run the lab.

20-minute prep plan

Time	Action
0–4 min	Skim the cheatsheet tables (sign convention, formulas, mistakes).
4–9 min	Re-read one worked example from the lecture summary — covering pen, write it out. Pick Example 4 (Alice ramp) if pressed.
9–14 min	Take the cheatsheet quiz. Don’t worry about score.
14–18 min	Skim the lab section of the lecture slides — know what data each part records.
18–20 min	Run through the lab-prep checklist below.

What to revise first

Most students slip on three specific things this week:

1. Forgetting $\cos \theta$ on an incline. $F_N=mg\cos \theta$, not $mg$. Then $F_{\text{fric}}=\mu mg\cos \theta$.
2. Treating spring work as $Fx$. Spring force is not constant — use $\frac{1}{2}k{x}^2$ or the triangle area.
3. Mechanical-energy conservation with friction present. The simple $K{E}_i+P{E}_i=K{E}_f+P{E}_f$ is wrong if friction acts. Use the full balance.

Key formulas

$W=|F|\cos \theta \cdot |s|\text{(constant force)}W=\int F(s)ds\text{(variable)}$

$KE=\frac{1}{2}m{v}^{2}P{E}_g=mghP{E}_{\text{spring}}=\frac{1}{2}k{x}^2$

$P=\frac{\Delta W}{\Delta t}{F}_{\text{fric}}=\mu mg\cos \theta$

$\boxed{K{E}_i+P{E}_i+W_{\text{on-system}}=K{E}_f+P{E}_f+W_{\text{by-system}}}$

Likely workshop / lab tasks

Task type	What the setup usually looks like
Spring constant (Lab Part 1)	Hang masses on a spring, measure extensions, plot $F$ vs $x$, slope = $k$.
Coefficient of kinetic friction (Lab Part 2)	Tilt a ramp until the block slides at constant velocity, measure $\theta$, ${\mu }_k=\tan \theta$. Or apply a horizontal force and balance.
Cart displacement down a ramp (Lab Part 3)	Release cart from rest, measure displacement and time. Use energy balance to confirm ${\mu }_k$ or compute final $v$.
Portfolio energy problem	Multi-step balance with spring + ramp + friction (cf. Tutorial Exercise 5).
Conceptual exam question	”Why is $W=Fx$ wrong for a spring?” / “What’s the work done by a perpendicular force?”

Pre-lab checklist

• You can write $F_{\text{fric}}=\mu mg\cos \theta$ without looking it up.
• You know that the slope of an $F$ vs $x$ line for a spring is the spring constant $k$.
• You can derive ${\mu }_k=\tan \theta$ at the angle where a block slides at constant velocity (force balance along the slope).
• You have a method for reading off $k$ from a graph (slope = $\Delta F/\Delta x$, use two well-spaced points, not adjacent ones).
• You know the SI units: force in N, extension in m (not cm!), $k$ in N/m.

Mistakes to avoid

• Energy “lost” in a conservative system. It isn’t lost — it has just changed form. The numbers must balance to within experimental error.
• $F_N=mg$ on a slope. Wrong — it’s $mg\cos \theta$.
• Reading lab extension in cm and forgetting to convert. Always SI in your calculation.
• Using one trial for $k$ or ${\mu }_k$. Take multiple data points and use a fitted slope (or average).
• Confusing static and kinetic friction coefficients — the lab measures kinetic (${\mu }_k$).
• Reporting answers without units. Lab markers strip points for unit-less results.

Mini self-test

Try these without notes. Five minutes total.

1. A horizontal force of $40\text{N}$ pushes a $5\text{kg}$ box $3\text{m}$ across a floor with ${\mu }_k=0.2$. (a) Work done by the applied force. (b) Work done by friction. (c) Final KE if it started from rest.
2. A spring with $k=250\text{N/m}$ stores $45\text{J}$. What is its compression?
3. A $2\text{kg}$ ball drops $1.8\text{m}$ onto a spring of constant $k=800\text{N/m}$. Ignoring air resistance and the small spring compression height, find the maximum spring compression.

Answers:

Question	Answer
1	(a) $W_{\text{APP}}=40\times 3=120\text{J}$; (b) $W_{\text{fric}}=0.2\times 5\times 9.8\times 3=29.4\text{J}$ (energy out); (c) $K{E}_f=120-29.4=90.6\text{J}$
2	$\frac{1}{2}k{x}^2=45\Rightarrow x=\sqrt{2\times 45/250}=\sqrt{0.36}=0.6\text{m}$
3	$mgh=\frac{1}{2}k{x}^2\Rightarrow x=\sqrt{2mgh/k}=\sqrt{2\times 2\times 9.8\times 1.8/800}\approx 0.297\text{m}$

Done checklist

• Read the cheatsheet tables.
• One worked example from the lecture, copied out longhand (recommended: Alice ramp).
• Cheatsheet quiz attempted.
• Mini self-test attempted.
• Pre-lab checklist completed.
• Lab worksheet template printed/open and ready.

That’s it. Bring a calculator, a pen, and SI units.

Source files used

• EGD102-Physics/Lecture6_CTP1.pdf — lecture slides (including lab structure slides 26–28)
• EGD102-Physics/EGD102 - Lecture6 - Notes.pdf — handwritten worked solutions
• EGD102-Physics/Tutorial 6.pdf — five exercises
• EGD102-Physics/Tutorial 6_Solutions.pdf — solutions including the three-methods spring exercise