Exercício de Dinamica Aplicada (207)

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368 
 
 
PROBLEM 12.44 
A 130-lb wrecking ball B is attached to a 45-ft-long steel cable 
AB and swings in the vertical arc shown. Determine the tension 
in the cable (a) at the top C of the swing, (b) at the bottom D of 
the swing, where the speed of B is 13.2 ft/s. 
 
SOLUTION 
(a) At C, the top of the swing, 0;Bv = thus 
 
2
0B
n
AB
v
a
L
= = 
 0: cos 20 0n BA BF T WΣ = − ° = 
 or (130 lb) cos 20BAT = × ° 
 or 122.2 lbBAT =  
(b) 
2( )
:Σ = − = B D
n n BA B B
AB
v
F ma T W m
L 
 or 
2
2
130 lb (13.2 ft/s)
(130 lb)
45 ft32.2 ft/s
BAT
   = +         
 
 or 145.6 lbBAT = 