Laws of Motion

Question
CBSEENPH11020871

A cylinder rolls up an inclined plane, reaches some height and then rolls down (without slipping throuhgout these motions). The directions of the frictional force acting on the cylinder are

  • Up the incline, while ascending and down the incline while descending

  • Up the incline, while ascending as well as descending

  • down the incline, while ascending and up the incline while descending

  • Down the incline while ascending as well as descending.

Solution

B.

Up the incline, while ascending as well as descending

It is obvious that during ascending, a retarding i.e. anticlockwise moment is required. I should be remembered that torque due to friction has the same sense the angular acceleration.

Question
CBSEENPH11020879

A long block A of mass M is at rest on a smooth horizontal surface.  A small block B of mass M/2 is placed on A at one end and projected along A with same velocity v. The coefficient of friction between the block is μ. Then the acceleration of blocks A and B before reaching a common velocity will be respectively

  • μg2 (towards right), μg2 (towards left)

  • μg (towards right), μg (towards left)

  • ug2 (towards right), μg (towards left)

  • μg (towards right), μg2 (towards left)

Solution

B.

μg (towards right), μg (towards left)

The force causing the motion of A is a frictional force between A and B,

So, acceleration of A

μMB g = MAaA aA = μ MBMA g = μg2 (towards right)

Block B experiences frictions force towards the left.

MBaB = μMBg ⇒aB = μg towards left

Question
CBSEENPH11024908

State Hooke's Law.

Solution

Hooked law states that for a small force, Stress is directly proportional to strain. the constant of proportionality is the modulus of elasticity

Question
CBSEENPH11024909

State Boyle's Law

Solution

Boyle’s law is a gas law which states that the pressure exerted by a gas (of a given mass, kept at a constant temperature) is inversely proportional to the volume occupied by it. In other words, the pressure and volume of a gas are inversely proportional to each other as long as the temperature and the quantity of gas are kept constant. Boyle’s law was put forward by the Anglo-Irish chemist Robert Boyle in the year 1662.

For a gas, the relationship between volume and pressure (at constant mass and temperature) can be expressed mathematically as follows.

P ∝ (1/V)

Where P is the pressure exerted by the gas and V is the volume occupied by it. This proportionality can be converted into an equation by adding a constant, k.

P = k*(1/V) ⇒ PV = k

The pressure v/s volume curve for a fixed amount of gas kept at constant temperature is illustrated below.

It can be observed that a straight line is obtained when the pressure exerted by the gas (P) is taken on the Y-axis and the inverse of the volume occupied by the gas (1/V) is taken on the X-axis.