When two protons collide they tend to bounce off each other because of their electromagnetic repul$-$sion.But if they getclose enough,the strong force takes over and they fuse together. The exact prob$-$ability of fusing depends in a complicated way on their energies and involves tunneling probabilities, but as a reasonable model we can say that they will fuse if they have enough energy to come within $1\mathrm{.}851014$ mofeachother.

$($a$)$ How much kinetic energy must two protons have in order to collide and fuse?