Which of the following figure represents damped harmonic motion?

(i)
(ii)
(iii)
(iv)

1. (i) and (ii)

2. (iii) and (iv)

3. (i), (ii), (iii), and (iv)

4. (i) and  (iv)

The damping force on an oscillator is directly proportional to the velocity.The units of the constant of proportionality are 

(1)$kg m{s}^{-1}$                               

(2)$kg m{s}^{-2}$

(3)$kg s^{-1}$                                   

(4)$kg s$

 Amplitude of a wave is represented by

$A=\frac{c}{a+b-c}$

Then resonance will occur when

(1)     $b=-c/2$              

(2)         b = 0 and a =  c

(3)     $b=-a/2$              

(4)         None of these

Which of the following figure represent(s) damped simple harmonic motions?

1. 

2. 

3. 

4. 

The amplitude of the damped oscillator becomes (1/3) in 2s. Its amplitude after 6s is 1/n times the original. Then n is equal to:

1. $2^3$

2. $3^2$

3. $3^{1/3}$

4. $3^3$