Question

Consider a 7.0-kg red block pressed against a wall falling at -2.5 m/s. Given the following coefficients between the wall and the block--μk = 0.4 and μs = 0.7, determine the force of the hand that acts on the block. Use g = 9.79 m/s

Answer 1

The block is falling at a constant rate; that is not accelerating. Hence the net force on the block--\( F_g \) for gravity and \( F_f \) for friction must cancel.

Now as \( F_f = \mu N \), where \( N \) here is the normal force of the wall against the block, that must be the force supplied by the hand. Hence you need to solve for the magnitude of \( N \) given that
\[ F_g + F_f = 0 \]