Fluids and Newton's Laws (Buoyancy)

AP Physics 1· difficulty 2/5

T F_B W

The diagram shows a submerged block in static equilibrium, held in place by string tension TT, with buoyancy FBF_B and weight WW acting on it. Which equation correctly relates these forces?

  • A

    T+FB=WT + F_B = W

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  • B

    T+W=FBT + W = F_B

  • C

    T=FB+WT = F_B + W

  • D

    T=WFBT = W - F_B, only if W>FBW > F_B

Explanation

Equilibrium (up positive): T+FBW=0T+FB=WT + F_B - W = 0 \Rightarrow T + F_B = W (assuming the block is denser than the fluid so the string must pull up to keep it from sinking).

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