Online Course Discussion Forum
Question 7 & 8 Physics
Thanks for your patience.
For Question 7, recall a Bq is just 1 decay per second, so the question is just asking if there are currently on average 1.75 decays per second for the sample. This problem is somewhat similar to example 30-9 in the book (this example solves for the number of decays, we want to instead solve for the time)
For Question 8, Table 30-1 gives the different masses of protons, electrons, and neutrons in various units. Note when measuring the masses we want to give the neutral atoms, so we either use electrons as well or use the mass of hydrogen (as given in that table) for the calculation. Note the actual mass is less because of binding energy, which is why the question is worded as "less than or equal to".
Hope this helps!