Answer:
The force is 
Explanation:
From the question we are told that
The mechanical advantage is
The load is
The height is 
Generally mechanical advantage is mathematically represented as

Here E is the force that must be applied to move the piano
=> 
=> 
=> 
Answer:
1. Torque → F. Study of forces
2. C.O.G → D. Point of action of weight.
3. Plumb line → A. Line of C.O.G
Same speed, because mass is neglected. The things that affect the speed are the distance and speed of the rock.