A board of mass $m$ lies on the ground. What is the magnitude of the force you would have to exert to lift one end of the board barely off the ground (assuming that the other end still touches the ground)?
A) $2 m|\vec{g}|$
B) $m|\vec{g}|$
C) $1 / 2 m|\vec{g}|$
D) The answer depends on the board's length.
E) Other (explain)

Question

Quizplus · Accepted Answer

To lift one end of the board barely off the ground, you need to exert a force equal to half the weight of the board, because you are effectively lifting half the mass of the board. The weight of the board is $m|\vec{g}|$, so half of this weight is $1 / 2 m|\vec{g}|$.

A Board of Mass mmm Lies on the Ground 2m∣g⃗∣2 m|\vec{g}|2m∣g​∣ B) m∣g⃗∣m|\vec{g}|m∣g​∣

A Board of Mass $m$ Lies on the Ground $2 m|\vec{g}|$ B) $m|\vec{g}|$