Two balls of equal mass have a head on collision with speed $4 {\mathrm{ms}}^{-1}$ each travelling in opposite directions. If the coefficient of restitution is 1/2, the speed of each ball after impact will be

• A

  $1 {\mathrm{ms}}^{-1}$

• B

  $2 {\mathrm{ms}}^{-1}$

• C

  $3 {\mathrm{ms}}^{-1}$

• D

  data insufficient