Explanation:
Assuming the wall is frictionless, there are four forces acting on the ladder.
Weight pulling down at the center of the ladder (mg).
Reaction force pushing to the left at the wall (Rw).
Reaction force pushing up at the foot of the ladder (Rf).
Friction force pushing to the right at the foot of the ladder (Ff).
(a) Calculate the reaction force at the wall.
Take the sum of the moments about the foot of the ladder.
∑τ = Iα
Rw (3.0 sin 60°) − mg (1.5 cos 60°) = 0
Rw (3.0 sin 60°) = mg (1.5 cos 60°)
Rw = mg / (2 tan 60°)
Rw = (10 kg) (9.8 m/s²) / (2√3)
Rw = 28 N
(b) State the friction at the foot of the ladder.
Take the sum of the forces in the x direction.
∑F = ma
Ff − Rw = 0
Ff = Rw
Ff = 28 N
(c) State the reaction at the foot of the ladder.
Take the sum of the forces in the y direction.
∑F = ma
Rf − mg = 0
Rf = mg
Rf = 98 N
That's a great idea ! A wind turbine (windmill) or solar panels
on the roof of every WalMart, but don't stop there. Let K-Mart,
Target, Sears, Macy's, 7-11, McDonald's, and Subway in on it too.
In fact, why not place them on the roof of every house and
apartment building too ?
Just one question: Who's going to pay for them ?
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The biggest single year-round residential use of energy in the
USA is to heat up and keep a ready supply of hot water. So the
single biggest residential use of energy could be eliminated with
a simple solar water heater on the roof of every house. From my
own personal observation, I know that Israel is there now, but here
in the USA, it's apparently not worth the time, effort, or expense ! ? !
