In his tests
59%
10 of 17 right · room 55%
Chapter tests
–
Past papers
2/11
2 right · 0 wrong · 0 starred
Revisions
0
none yet
Marks lost
−4
to wrong answers in tests
Time a question
2m 13s
average in tests
Against the room
Share right on these exact questions, in his tests. His batch is the closer comparison.Him
59%
His batch
55%
Everyone who sat it
54%
Why they went wrong
His reasons on 6 of 7 not right.
Concept gap 4Careless 1Time trap 1
Chapter tests and sets
Chapter tests and the sets sat in Plus4 on this chapter. The score is his questions on this chapter only. Tap one to go over it.1 sitting, newest first
Short notes
Formulas, traps, what to remember. Every version is kept. The coach adds a trap when his tests show one the note misses, and says why.Revised by the coach 14 Nov: Added the trap from the torque doubt; closed by the twin set · 2 versions
1 · Formulas and when each holds
- τ = r × F, with r from the point the torque is taken about.
- τ = Iα about a fixed axis, or about the centre of mass.
- L = Iω about a fixed axis; L is conserved when the net external torque is zero.
- Rolling without slipping: v = ωR, KE = ½mv²(1 + k²/R²).
- Parallel axis: I = I_cm + Md².
2 · Question types and the first step
- Rolling down an incline: write a = g sin θ / (1 + k²/R²) first.
- Collision with a rod: conserve angular momentum about the pivot, not linear momentum.
3 · Traps
Parallel axis: d is the distance between parallel axes, never along the axis.
Torque about a point: he took r from the axis instead of from the point asked about. Rule: mark the point first, draw r from it.
4 · My additions
- Draw the axis before writing any I.
His questions on this chapter
Newest first. Tap a question to open it.19 from tests and sets · 7 not right
Every time it came up
6 Sep 2026
13 Sep 2026
20 Sep 2026
4 Oct 2026
11 Oct 2026
25 Oct 2026
1 Nov 2026
5 Nov 2026
8 Nov 2026
14 Nov 2026
RightWrongSkippedStarredToo few to read a trend into: read the dots, not a slope.
Concept gaps
A gap closes only when he answers an unseen question on it right, on a later day.0 open
Closed or dropped · 1
- Torque about a point off the axis of rotationClosed 14 NovFound 13 Nov in a doubt · 4 marks at riskCloses on an unseen question answered right on a later day.Closed by an unseen question answered right: see it
His doubts
Newest first, as the coach logged them.1 on this chapter
- Torque of a force about a point that is not on the axis of rotationSolved with hints13 Nov · Class module, rotation exercise · Concept gap · torque about a point off the axis · 2 steps of help · 14 minHe had tried: Took the perpendicular distance from the axis instead of from the point.The key idea, in his words: Torque about a point is r × F with r drawn from that point; the axis does not enter.
The whole conversation
- Where he stopped: used the distance from the axis, got the wrong magnitude.
- Hint 1: which point is the torque asked about? He saw it was the corner, not the centre.
- Hint 2: draw r from that corner to where the force acts. He did, and took r × F.
- Answer: right on his own after that.
Revisions
None logged.