Question

the lungs performs 2.4j of work during each expansion . how many times per minute do they expand if their power is 2 j/s ?

Answer 1

P = 2 j/s
work done during expansion = 2.4 j ( W ) 
t = 1 minute = 60 seconds

$P = \frac{W}{t}$
   W = P * t
       = 2 * 60 = 120 J
total no. of expansion per minute = 120 / 2.4 = 50 ( answer )

Answer 2

power ( p ) = 2 j/s
time = 1min = 60s
work done during each expansion = 2.4j
Work done = power * time
     = 2 *60 = 120j
therefore , number of expansion per minute = 120/2.4
                                                               = 50