A ball of radius r and density dropped through a viscous liquid of density and viscosity attains its terminal velocity at time t, given by t = A a rb c d, where A is a constant and a, b, c and d are integers. The value of b + ca + d is .
Answer
1
Solution
Dimensions: [ ] = [ ] = ML-3, [r] = L, [ ] = ML-1T-1
T = ( ML-3)a+d Lb ( ML-1T-1)c
T: -c = 1 c = -1
M: a + d + c = 0 a + d = 1
L: -3(a + d) + b - c = 0 b = 3 - 1 = 2
b + ca + d = 2 - 11 = 1
(Check: time constant = m6 r = 2 r29 , i.e. a = 1, b = 2, c = -1, d = 0.)
Answer: 1