A person throws an object on a horizontal frictionless plane surface. It is noticed that there are two forces acting on this object— (i) gravitational pull and (ii) normal reaction of the surface. According to the third law of motion, the net resultant force is zero. Which one of the following can be said for the motion of the object ?
- AThe object will move with acceleration.
- BThe object will move with deceleration.
- CThe object will move with constant speed, but varying direction.
- DThe object will move with constant velocity.
Explanation
With no friction, the horizontal forces on the object sum to zero, while gravity and the normal reaction cancel in the vertical direction. By Newton's first law, zero net force means the object maintains its existing state of motion — it moves with constant velocity, i.e., uniform speed in a straight line. It can neither accelerate nor decelerate, and it certainly does not stop. The object therefore moves with uniform speed.