A firecracker breaks up into two pieces, one of which has a mass ...

[yoroshambo]

A firecracker breaks up into two pieces, one of which has a mass of 200 g and flies off along the +x-axis with a speed of 82.0 m/s. The second piece has a mass of 300 g and flies off along the +y-axis with a speed of 45.0 m/s.
 
  What is the total momentum of the two pieces? A) 361 kg  m/s at 56.3 from the +x-axis
  B) 93.5 kg  m/s at 28.8 from the +x-axis
  C) 21.2 kg  m/s at 39.5 from the +x-axis
  D) 361 kg  m/s at 0.983 from the +x-axis
  E) 21.2 kg  m/s at 56.3 from the +x-axis

Question 2

An electron has a relativistic momentum of 1.1  10-21 kg  m/s. What percent of its total energy is its kinetic energy?
 
  (melectron = 9.11 10-31 kg, c = 3.0  108 m/s)

[cdmart10]

Answer to Question 1

C

Answer to Question 2

76

[yoroshambo]

Thanks for the timely response, appreciate it

[scikid]

Great answer, keep it coming