In a Particle Accelerator, Protons Are Fired at a Stationary

Multiple Choice

In a particle accelerator, protons are fired at a stationary target and collide elastically with the nuclei of the atoms in the target. In one such experiment, a beam of protons is fired with a speed of 2.10 × 10⁷ m/s. The protons that undergo a collision rebound with a speed of 1.68 × 10⁷ m/s. What is the mass of the nuclei that the protons are colliding against?

A) 6.00 proton masses
B) 7.00 proton masses
C) 8.00 proton masses
D) 9.00 proton masses
E) 10.0 proton masses