Applications of Newton’s Laws

(a)        When objects are in equilibrium

To solve problems involving objects in equilibrium:

Step 1: Make a sketch of the problem.

Step 2: Isolate a single object and then draw the free-body diagram for the object. Label all external forces acting on it.

Step 3: Choose a convenient coordinate system and resolve all forces into x and y components.

Step 4:Apply the equations and .

Step 5:Step 4 will give you two equations with several unknown quantities. If you have only two unknown quantities at this point, you can solve the two equations for those unknown quantities.

Step 6:If step 5 produces two equations with more than two unknowns, go back to step 2 and select another object and repeat these steps.

Eventually at step 5 you will have enough equations to solve for all unknown quantities.\

Question :A ‘block’ of mass 10 kg is suspended with string as shown in figure. Find tension in the string.

(g = 10 m/s2).

Answer:

F.B.D. of block

Fy = 0

T – 10 g = 0

therfore         T = 100 N