Old Spec Extra

Question 1

How to show that a plane is smooth or not using momentum ideas? When a particle collided with the floor and bounces off at an angle

Answer 1

The only force that would act at the particle with the floor is FRICTION, so consider x direction momentum only

If this is cinserved the plane is smooth

If not then the floor has been moved, friction is acting thus, and not smooth

Question 2

How to find the INTERNAL forces of rods when a system is at equilibrium?

Answer 2

Go at the specific intersection points, and equate all forces there to 0

Be tactful about it, choose points which have least unknowns
- remember these forces include reactions etc

Question 3

When taking moments, do we include the force due to internal forces on rods etc?

Answer 3

No, unless there mass, but if they weightless, all their tensions and compressions should CANCEL OUT EACH OTHER, so we don’t take them

Question 4

Be careful, if some mass falls off WITHOUT any velocity, and no horizontal force acting on something, what will be final velocity

Answer 4

Will be the same, as no force so Newton 2nd law

Question 5

Centre of mass cylinder pornlem…