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# Imagine you are standing on a cardboard box that is only just strong enough to support your weight. What would happen to it if you tried to jump into the air? The cardboard box would

(A) be unaffected $\quad$ (B) collapse $\quad$ (C) move sideways $\quad$ (D) move up as well

Toolbox:
• According to Newton's second law: When viewed from an inertial reference frame, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
When you try to jump into the air, you have to accelerate yourself vertically. Since there is an upward force on your body, $F_u$ for the upward acceleration, there must be an equal and opposite downward force on the box.
According to Newton's 2nd law $\large \Sigma$$F = F_u - mg = ma \rightarrow F_u = mg + ma$
Thus, the force downward on the box is greater than your weight, and is therefore greater than what the box can support.
Therefore the box will collapse.
edited Aug 19, 2014