6. Consider two carts, of masses m and 2m, at rest on a frictionless air track. If you push the lower-mass cart for 3 s and then the other cart for the same length of time and with the same force, which cart undergoes the larger change in momentum? (A) The cart with mass m. (B) The cart with mass 2m. (C) Same for both carts. (D) It is not possible to tell from the information given.