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The velocity-time graph shown models the motion of a parachutist falling vertically. There are four stages in the motion:

- falling freely with the parachute closed,
- decelerating at a constant rate with the parachute open,
- falling with constant speed with the parachute open,
- coming to rest instantaneously on hitting the ground.

a) Show that the total distance fallen is $1048{\text{ }}m$.

The weight of the parachutist is $850{\text{ }}N$.

b) Find the upward force on the parachutist due to the parachute, during the second stage.

پاسخ تشریحی :
نمایش پاسخ

a) $\left[ {{\raise0.5ex\hbox{$\scriptstyle 1$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}5 \times 50 + {\raise0.5ex\hbox{$\scriptstyle 1$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}7\left( {8 + 50} \right) + 90 \times 8} \right]$

Distance is $1048{\text{ }}m$

b) $a = \left( {8 - 50} \right)/\left( {12 - 5} \right)$ or $d = \left( {50 - 8} \right)/\left( {12 - 5} \right)$

$850 - F = 85a$ (or $ - 85d$)

Upward force is $1360{\text{ }}N$

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