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Kinematics

Problem 1.3

A car starts moving rectilinearly, first with acceleration ww =5.0 m/s2=5.0 \mathrm{~m} / \mathrm{s}^{2} (the initial velocity is equal to zero), then uniformly, and finally, decelerating at the same rate ww, comes to a stop. The total time of motion equals τ=25\tau=25 s. The average velocity during that time is equal to ⟨v⟩=72 km\langle v\rangle=72 \mathrm{~km} per hour. How long does the car move uniformly?

Reveal Answer
Δt=τ1−4⟨v⟩/wτ=15 s\Delta t=\tau \sqrt{1-4\langle v\rangle / w \tau}=15 \mathrm{~s}
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