Kara and John are pushing their grocery carts along a flat surface in a store. Kara's cart is empty, and John's cart is full.

Kara and John each push their cart with the same force. Why does Kara's cart speed up more than John's cart when they push with the same force?

A.

because no gravity is acting on her cart

B.

because her cart has less mass

C.

because her cart needs no force to push it

D.

because her cart has more friction acting on it