Question

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?

Answer 1

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