The force diagram for the situation 1 and situation 2 is shown in the image attached.
The equation for situation is F - Fs = ma and the equation for the situation 2 is F₃ + F₁cos(θ₁) + F₂cos(θ₂) - Fs = ma.
How to draw the force diagram for each situation?
Situation 1: You are trying to help your mom move her piano.
The force applied by you and your mom is in the same direction.
The forces include;
- Total force applied by you are your mom (F)
- The force of friction preventing the motion (F)
F - Fs = ma
where;
- m is the mass of the piano
- a is the acceleration of the piano
Situation 2: You are pulling on the piano up and to the right, your mom is pushing on the piano down and to the right, and your dad is pushing up and to the right.
The forces include;
- weight of the piano acting downwards (W)
- normal force of the piano (N)
- Your applied force (F1)
- the father's applied force (F2)
- the mom's applied force (F3)
- Force of friction opposing the motion (Fs)
The equation of the forces in horizontal direction is;
F₃ + F₁cos(θ₁) + F₂cos(θ₂) - Fs = ma