A simple pendulum is vibrating with an angular amplitude of 90 0 as shown in the adjoining figure. For what value of 
, is the acceleration directed
(i) Vertically upwards?
(ii) Horizontally?
(iii) Vertically downwards?
A
0 0 cos –1 
, 90 0
, 90 0
B
90 0 , cos –1 
, 0 0
, 0 0
C
cos –1 
, 0 0 , 90 0
, 0 0 , 90 0
D
cos –1 
, 90 0 , 0 0
, 90 0 , 0 0
Text Solution
Verified by ExpertsThe correct answer is:
A
Acceleration is downward at α = 90 0 and it is upward at α = 0 0 Acceleration is horizontal where, T cos α = mg
⇒ T = 
... (1)
∴ T = 
= 2 mg = 3 mg cos α
∴ cos 2 α = 
⇒ α = cos –1 
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