Answer:
man will move in opposite direction with speed

Explanation:
As we know that man is lying on the friction-less surface
so here net force along the surface is zero
so if we take man + stone as a system then net change in momentum of this system will become zero
so here we have


here we have



Answer: 1.2m/s^2
Explanation: the force exerted on the car is 900N upwards
The mass of the car is 750kg
According to Newton's third law acceleration is proportional to force
F = ma
900 = 750a
a = 900/750
a = 1.2m/s^2