Question

When no friction is involved, what can an outside force do to a moving object?

a. nothing
b. change the object's speed only
c. change the object's direction only
d. change the object's speed or direction

Answer 1

When friction IS present, it's possible that if the outside force
isn't strong enough or is in the wrong direction, then it might
have no effect on the object's motion.

But when NO friction is involved, an outside force MUST change
the object's speed or direction. It can't help it.