Q135 / 150 · MHT CET 2019 (Shift 1) · Physics

Eight identical drops of water falling through air with uniform velocity of 10cm/s combine to form a single drop of big size, then terminal velocity of the big drop will be

  • A
    80 cm/s
  • B
    10 cm/s
  • C
    30 cm/s
  • Correct answer
    D
    40 cm/s

Solution

Given, terminal velocity of each small drop
v1=10cms
When 8 small drops are combined to form bigger
If r1 be radius of small drop and r2 be radius of bigger drop, then v2=v1
43πr23=8×43πr13⇒r2=2r1
∴ Terminal velocity of the drop
v=2r29p-σ9η
i.e., v∝r2
∴v1v2=r12r22=r122r12⇒v1v2=14
v2=4v2=4×10=40

Hence, the correct answer is option: 'D'.

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