Question

The amount of force needed to keep a 0.5kg baseball moving at a constant speed of 4 m/s on frictionless ice is

Answer 1

$$F=ma=0.5(0)=0\ N$$

Since the speed is constant, velocity is constant (assuming itis moving in a straight line) acceleration is zero. Hence force is zero. Since there is no friction, no force is there to stop it. The body moves by virtue of inertia of motion.