Problem 14.75 The 2-kg mass m rotates around the
vertical pole in a horizontal circular path. The angle θ =
35◦ and the length of the string is L = 1 m. What is the
magnitude of the velocity?
θ
L
Strategy: Notice that the vertical acceleration of the
mass is zero. Draw the free-body diagram of the mass
and write Newton’s second law in terms of tangential
and normal components.
m
Solution:
35°
m = 2 kg
ez
◦
r = L sin 35
er
r = 0.574 m
Fr = −T sin 35◦ = −mv 2 /r
mv2/r
mg
Fz = T cos 35◦ = mg
Two eqns, two unknowns (T, V)
Solving,
T = 23.95 N
θ
L
r = 1.98 m/s
r
m