Tom is a hefty guy with a good sense of balance who wants to push
down a brick wall. The wall, however, is strong enough to withstand a
horizontal push of 2000 N and Tom can only exert a push of about his
1000 N weight with his muscles. Fortunately, Tom has a perfectly
rigid 
beam (of negligible mass), and there is a solid rock
(that can withstand essentially any push) 5 m from the wall to brace
it on. Even more fortunately, Tom has taken physics 51! He therefore
cuts the beam to lean against the house as shown and proceeds to walk
up the beam towards the house.
a) Suppose the coefficient of static friction between the beam and the
wall is 0.4. What is the highest Tom can make the point of contact of
the beam with the wall (
) and still knock it down if he walks to the
end?
b) Tom is smart, and uses some grease and a smooth braceplate to render the brick wall ``frictionless'' where the beam hits it. He then cuts the beam so that it rests 1.5 m up on the wall. How far must he walk (horizontally) before the wall breaks?