Engineering Board Exam Reviewer · Applications: Newton's Second Law and Motion · hard
A 2-kg object falls from rest (g=9.81 m/s2) against an air resistance of 0.05v2 newtons. Find its speed after 2 seconds.
- 19.6 m/s
- 19.8 m/s
- 9.1 m/s
- 15 m/s
Answer
D. 15 m/s
Solution
dv/dt=9.81-0.025v2. The terminal speed is vt=sqrt(9.81/0.025) 19.81 m/s and the solution from rest is v=vt ≤ft(gt/vt ). At t=2: v=19.81 (0.990) 15.0 m/s.
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