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A thin flat plate 0.5 m × 0.7 m in size settles in a large tank of water with a terminal velocity of 0.12 m/s. The co-efficient of drag
for a laminar boundary layer andCD = 1.328 √RL = 0.072 (RL)1 / 5
for a tubulent boundary layer, where RL is the plate Reynolds number.
Assume μ = 10–3 N-s/m2 and r = 1000 kg/m3 The submerged weight fo the plate is
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- 0.0115 N
- 0.0118 N
- 0.0231 N
- 0.0376 N
Correct Option: C
| Reynold's number , RL = | ||
| υ |
| = | ||||
 |  | |||
| ρ | ||||
| = | ||||
| | |||
| 1000 | ||||
= 0.89 × 10–5
< 5 × 105
∴ Laminar boundary layer
| ∴ CD = | ||
| √RL |
| = | = 0.0046 | |
| √0.84 × 105 |
| Drag force , FD = CD . | ||
| 2 |
| = 0.0046 × | = 0.01159 N | |
| 2 |
Drag force for both sides of plates = 2 × FD
= 2 × 0.01159 = 0.0231 N
