Answer
(b) $\mu_s \geq 0.5$
Work Step by Step
The correct answer is: (b) $\mu_s \geq 0.5$
Since the heater doesn't budge when Tim pushes with a force of 400 N, the force of static friction must be 400 N. However, a force of 400 N is not necessarily the maximum possible force of static friction. Therefore:
$F_N~\mu_s \geq 400~N$
$(800~N)~\mu_s \geq 400~N$
$\mu_s \geq 0.5$
