Exercício de Dinamica Aplicada (40)

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201 
 
 
PROBLEM 11.CQ10 
A child walks across merry-go-round A with a constant speed u relative to A. The 
merry-go-round undergoes fixed axis rotation about its center with a constant 
angular velocity ω counterclockwise.When the child is at the center of A, as 
shown, what is the direction of his acceleration when viewed from above. 
(a) 
(b) 
(c) 
(d ) 
(e) The acceleration is zero. 
 
SOLUTION 
Polar coordinates are most natural for this problem, that is, 
 
2( ) ( 2 )ra r r r r θθ θ θ= − + +e e
    
 (1)
 
From the information given, we know 0, 0, 0, , .r r r uθ θ ω= = = = =-   When we substitute 
these values into (1), we will only have a term in the −θ direction. 
 
 Answer: (d ) 