Quarter-cycle rows make the sign pattern visible without hidden trigonometry. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Phase zero is the right turning state
Phase 0 gives position 4 m, velocity 0 metres per second, and acceleration -4 metres per second squared.
ϕ=0⇒x=4m,v=0m/s,a=−4m/s2
One quarter cycle trades displacement for velocity
Phase 1/4 gives position 0 m, velocity -4 metres per second, and acceleration 0 metres per second squared.
ϕ=41⇒x=0m,v=−4m/s,a=0m/s2
Half a cycle flips the endpoint signs
Phase 1/2 gives position -4 m, velocity 0 metres per second, and acceleration 4 metres per second squared.