A car covers half of a journey with speed v. The remaining half is divided into two equal distances which are covered with speeds 2v and 4v. The average speed is:
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A car covers half of a journey with speed v. The remaining half is divided into two equal distances which are covered with speeds 2v and 4v. The average speed is:

G1 Physics · Accepted Answer

Let total distance be D. Times: D/2 at v → D/(2v) D/4 at 2v → D/(8v) D/4 at 4v → D/(16v) Total time = D/v [1/2 + 1/8 + 1/16] = 11D/(16v). Average speed = D / [11D/(16v)] = 16v/11.