Given :
Initial mass , a = 150 gm .
Half time ,
.
Final mass , x = 18.75 gm .
To Find :
The time taken to decay 18.75 gm .
Solution :
We know , time taken is given by :
Here , k is a constant given by :
Putting all given value in above equation :
We get :
Therefore , time taken is 6.94 hours .
Hence , this is the required solution .
Answer : The change in internal energy is, 900 Joules.
Solution : Given,
Heat given to the system = +1400 J
Work done by the system = -500 J
Change in internal energy is equal to the sum of heat energy and work done.
Formula used :
where,
= change in internal energy
q = heat energy
w = work done
As per question, heat is added to the system that means, q is positive and work done by the system that means, w is negative.
Now put all the given values in the above formula, we get
Therefore, the change in internal energy is 900 J.
The change in internal energy depends on the heat energy and work done. As we will change in the heat energy and work done, then changes will occur in the internal energy. Hence, the energy is conserved.