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202301130918 Solution to 2011-IBHL-PHY-I-3

A skydiver of mass 80\,\mathrm{kg} falls vertically with a constant speed of 50\,\mathrm{m\,s^{-1}}. The upward force acting on the skydiver is approximately

A. 0\,\mathrm{N}.
B. 80\,\mathrm{N}.
C. 800\,\mathrm{N}.
D. 4000\,\mathrm{N}.

Roughwork.

As always start with a free-body diagram.

Take upward positive. Write the equation of motion by Newton’s 2nd law:

\begin{aligned} \mathbf{F}_{\textrm{net}} & = m\mathbf{a} \\ f-mg & = m(0) \\ f & = mg \\ & \approx (80)(10) \\ & = 800 \\ \end{aligned}

And the answer is C.

This problem is not to be attempted.