The correct option is (c) 2 and 3 only.
Explanation
In physics, Work is defined as the product of the force applied and the displacement of the object in the direction of the force. The formula is W = F × d × cosθ, where F is the magnitude of force, d is displacement, and θ is the angle between the force and displacement vectors. For work to be done, there must be a non-zero displacement.
Statement-wise Analysis:
- Situation 1: Incorrect.
Although the girl applies a force, the trolley does not move. Since the displacement (d) is zero, the product F × d is zero. Therefore, scientifically, no work is done. - Situation 2: Correct.
When lifting a heavy load, the person applies an upward force to overcome gravity, and the load moves upwards (displacement occurs). Since both force and displacement exist and are in the same direction, work is done by the person. - Situation 3: Correct.
Moving a satellite from a lower orbit to a higher orbit requires energy to overcome the Earth's gravitational pull. An external force (via thrusters) must act on the satellite over a distance to increase its potential energy and shift its position. Consequently, work is done during this transfer. (Work done by gravity on a satellite moving in a stable circular orbit is zero, but changing orbits involves displacement against the field).
Key Takeaway:
Work is said to be done only when a force results in the displacement of an object. If there is no displacement, or if the displacement is perpendicular to the force, the work done is zero.