Question

A: when an object is placed on a surface the frictional force between the surface and the object is more if the mass of the object is heavy. R: static friction is directly proportional to normal reaction.

Whenever a body moves or tends to move over the surface of another body, a force comes into play which acts parallel to the surface of contact and opposes the relative motion. This opposing force is called friction. Static friction fS opposes the impending relative motion while the kinetic friction fK opposes the actual relative motion. Static friction is a self-adjusting force. The maximum value of static friction (fS=μsN) which comes into play when a body just starts moving over the surface of another body is called limiting friction. fs ≤ μsN and fk = μkN where N is the normal reaction between the two surfaces in contact. Both static and kinetic friction are independent of the area of surfaces in contact.

A body of mass m is moving with an acceleration 'a' under the action of a force 'g/4'. The weight of the body is

Force produces an acceleration of a₁ in a body and the same force produces an acceleration of a₂ which is twice to a₁ in another body. If the two bodies are combined and the same force is applied on the combination, the acceleration produced in it is