PHYSICS – Homework Chp. 10 – Part I. pg. 220-222
Concept review # 3. Problems # 1-3, 5
Concept Review
3.
Location of the fulcrum – for 1st class, fulcrum is between input and output force; for 2nd
class, output force is located between fulcrum and input force; for 3rd class, the input force is
located between fulcrum and output force.
Problems
1.
The cart is being pulled at constant velocity, so there the net F in the x-direction is equal
to zero.
ΣFx = 0 = Fcosθ - Ff
Ff = Fcosθ
500 N = Fcos(12°)
W = Fcosθ ∙ d
W = (500 N)(10 m) = 5000 J
2.
(a)
A first class lever has the fulcrum between the input and output force.
(b)
FiLi = FoLo
(80 N)(Li) = (200 N)(4 m)
Li = 10 m
3.
(a)
400 N / 4 ropes = 100 N / rope
(b)
MA = 4 = Li / Lo = Li / 3 m
Li = 12 m
(c)
5.
4
3 flights of stairs at 2 m per flight, so a total of 6 m
W = F x d = (50 N)(6 m) = 300 J