Question

estimate the percent error in measuring
a
a)distance of about 50 cm with a meter stick
b) a mass of about 1g with a chemical balance
c)time interval of about 4 mins with a stop watch

Answer 1

1.  the error in measurement could be 1mm. so percentage error is 
       (0.001 m / 0.50 m )*100 = 0.2%

2. chemical balance may have an accuracy of   0.1 mg   or 0.2 mg  , of that order.
       So  % error =  (0.1 mg /1000 mg) * 100 = 0.01%

3.  Let the minimum unit of measurement = 1 sec.  in the stop watch.
       % error = (1 sec / 240 sec)*100 = 0.4 %

   if the stop watch has a resolution of  0.1 sec, then
            % error  =   (0.1 / 240) * 100 = 0.04%