这句话中的系动词用得对吗？

没错。
但有其他错误：
美国人的复数应该是Americans，后面应该是where there is no car，用单数，或者there are no cars
no=not a（+单数）或者not any (+复数)

there are no cars

对啊
这是it做形式主语的句型啊
it is +形容词+to do

对，两个都对

it's hard to.... 强调句式
there is 。。。。做where引导的从句 is 要改成 are

顶楼上的楼上 hard换成 difficult car换成 vehicle就更好了

For Americans it's hard to imagine living in a place where there are no cars.