Constants Part A The drag force is an important fact of life for the small marin

Question

Constants Part A The drag force is an important fact of life for the small marine crustaceans called copepods. The drag force for small objects in water is very different from the drag force in air, so the drag equations of this chapter don't apply However, we can estimate the drag force from data. The velocity graph of (Figure 1) shows two phases of the swimming motion of a 2.1 mg copepod. First it swims vigorously, speeding up, then it slows down under the influence of drag What is the magnitude of the drag force? Express your answer to two significant figures and include the appropriate units al 7.4.10 N Submit Previous Answers Request Answer X Incorrect; Try Again; 5 attempts remaining Check your signs Part B What is the ratio of the drag force to the copepod's weight? Express your answer using two significant figures. Figure 0 0.10 0.20 0.30 0.40

Explanation / Answer

Part A -

m = 2.1 mg = 2.1 x 10^-6 kg

From the graph we can see that -

maximum velocity attained by the copepod, v = 0.70 m/s

Time taken to slows down the velocity to ero, t = 0.40 - 0.20 = 0.20 s.

So, retarding acceleration due to drag force, a = v / t = 0.70 / 0.20 = 3.5 m/s^2

So, magnitude of drag force, F = m*a = 2.1 x 10^-6 x 3.5 = 7.35 x 10^-6 N

In two significant figure, your answer is 7.4 x 10^-6 N

Part B -

ratio of drag force to the copepod's weight = F / mg = (7.35 x 10^-6) / (2.1 x 10^-6 x 9.81) = 0.357 = 0.36

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