Specific heat capacity and friction

[chanella35]

1. The tangential frictional force exerted by a band brakes on a rotating metal drum of circumference 0.25m is found to be 20N. If the mass of the drum is 0.4kg and its specific heat capacity is 0.35 kJ/kg K, calculate the number of complete revolutions of the drum are required to increase its temperature by 5.0 K.

Q= mcT
W=F*d

my attempt:

Q= mc[delta]T
W=F*d

f*d=mcT
20*d=400g*0.35*5
20d= 700
d=35
revolutions = 35/.25=140 or 1.4*10^2



^^^^^is that correct?

 

[kuruman]

revolutions = 35/.25=140 or 1.4*10^2
^^^^^is that correct?

No. If you have d, the number of revolutions is not d divided by the radius. It is d divided by the circumference. Also, it is a good habit to show the appropriate units every time you write down a number unless the number is dimensionless.