Revise: Work and Energy

W = Fd. No motion means no work, no matter the force.

150N over 4m → 600 J.

P = W/t — how quickly work is done.

24,000 J in 8s → 3000 W.

KE = ½mv². Doubling speed quadruples KE.

1000kg at 20m/s → 200,000 J.

GPE = mgh

15kg at 2m → 294 J.

Total energy is always conserved — only transforms between forms.

A falling ball: GPE converts entirely to KE.

Work and energy share the same unit: the joule.

80N over 3m → 240 J.

Power (W) is the RATE of energy transfer, not the total amount.

400W for 10s → 4000 J done.

Always square v before multiplying by ½m.

Tripling speed → 9× the KE.

GPE is always relative to a chosen reference height.

4kg at 5m → 196 J.

EPE = ½kx² — depends on the square of extension.

k=200N/m, x=0.15m → 2.25 J.

mgh = ½mv² for a freely falling object — mass cancels.

Dropped from 5m → v ≈ 9.9 m/s.