I've got some beef with how my last Physics III test was graded. I was hoping some of you might work out the following problems and post your answers to see if I had the right answers. Thanks!(adsbygoogle = window.adsbygoogle || []).push({});

1. Potassium 40 disintegrates by emitting a positron. What is the maximum energy for the emitted positron? Given information: potassium 40 mass is 39.96400 Da, rgon 40 mass is 39.962384 Da, and the electron mass is 5.4858 x 10^-4 Da.

EVERYBODY in the class got the same answer for this problem, and EVERYBODY was awarded 2 points out of 10, so I'm really curious to see if maybe the professor got the wrong answer.

2. A piece of charcoal contains 250 grams of carbon. It was found during an archaeological excavation. The carbon 14 activity was measured as 250 disintegrations in 1 minute. How old is this charcoal specimen? Given information: the half-life of carbon 14 is 5730 years, and the original fraction of carbon 14 was 1.3 x 10^-12.

I triple-checked my answer, and it also makes sense by estimation. Any help?

3. Two protons are moving with equal speeds but in directly opposite directions. They continue to exist after a head-on collision that produces a neutral pion. If the two protons and the pion are all at rest after the collision, find the initial speed of the protons. Energy is conserved in this collision. The mass of the pion is 2.40 x 10^-24 kilograms.

Thanks!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Beef with my last test

**Physics Forums | Science Articles, Homework Help, Discussion**