Neutrinos are hard to detect because
A) they experience only the gravitational force.
B) they move so fast.
C) they experience only the weak force.
D) they have such a small mass.
E) All of the above.
Question 2
Mort, who is standing on the ground, throws a ball at 20 m/s eastward as measured by him. What is the ball's velocity relative to Velma, who is in a train moving eastward past Mort at 70 m/s?
A) 50 m/s eastward
B) 90 m/s eastward
C) 50 m/s westward
D) 90 m/s westward
E) 70 m/s westward