A 38 kg child is sitting on a slide at angle 45o from the horizontal. What is the minimum value of static friction between the child and the slide that prevents the child from sliding down?
component of weight down slide = m g sin 45
component of weight normal to slide = m g cos 45
friction force = mu m g cos 45
remember cos 45 = sin 45
so
m g sin 45 = mu m g cos 45 = mu m g sin 45
mu = 1