Question

Work done when an object is slided on a horizontal ground?
A) Zero
B) Negative
C) Positive finite
D) Infinite

Answer 1

Total work done by a body is given by an expression $W = Fs\cos 90^\circ$where the force is the weight due to force of gravity. The angle between the force and motion of the body is $90^\circ$. And the value of $\cos 90^\circ = 0$. So according to the formula when the direction of motion is perpendicular to applied force then the total work done is zero.

Complete step by step answer:
When an object is slided on a horizontal ground, the total work done by the body because of its weight is zero. According to the formula $W = Fs\cos 90^\circ$, the work done is dependent on the angle between the direction of force and direction of motion. Since the value of $\cos 90^\circ = 0$ therefore the total work done is also zero. The weight of the body acts downwards pointing to the center of earth. It is known that $\theta = 90^\circ$and $\cos 90^\circ = 0$ therefore,
$W = F \times s \times 0$

Which gives total work done equals to zero. Other factors on which total work depends on are applied force and the displacement by the body. If force becomes zero or displacement is zero then also total work done is considered zero. The direction of force and displacement also changes the nature of work. If both are in opposite directions, the work is considered as negative work done. And if the direction is the same then work is called positive work done.

Note: When a body slides on a horizontal ground, we consider the surface as smooth and frictionless. This means that only the force of gravity acts on the body while sliding. If friction also comes into play then total work done by the body will be changed. Whenever the direction of force is perpendicular to motion of the body then the total work will be zero.