Mechanics

Question 1

Define centroid with examples

Answer 1

center of mass of a geometrical figure having uniform density. eg. centroid of triangle is the intersection of 3 medians of triangle.

Question 2

Define center of gravity with example

Answer 2

A point on an object where the distribution of weight is equal in all directions.
eg. center point of tennis ball

Question 3

define equilibrium

Answer 3

When multiple forces act upon a body and it still remains at rest it is said to be equilibrium

Question 4

define mechanical advantage & velocity ratio

Answer 4

ratio of the load (W) to the applied effort (P) used to lift the load.
the ratio of the distance traveled by the effort (y) to the corresponding distance traveled by the load (x)

Question 5

Define load and effort

Answer 5

The weight to be lifted by a machine

The force applied on a simple lifting machine to lift the load

Question 6

Define stress with its units

Answer 6

The applied force per unit cross-sectional area of a body is , measured in N/m² or Pa (Pascals).

Question 7

Define strain with its units

Answer 7

change in dimension per unit original dimension
No unit

Question 8

Define modulus of elasticity with units

Answer 8

Within the elastic limit the ratio of longitudinal stress to longitudinal strain is modulus of elasticity. N/m^2

Question 9

Define modulus of rigidity with its unit

Answer 9

ratio of shear stress to shear strain. Pascal

Question 10

Define bulk modulus with its unit

Answer 10

ratio of volume stress to volume strain

Question 11

Define simple lifting machine and compound machine

Answer 11

a simple machine that can lift heavy loads by applying a comparatively smaller effort.

combination of 2 or more simple machines working together.

Question 12

State relation between mechanical advantage velocity ratio and percentage efficiency

Answer 12

MA = VR / η

Question 13

Define effort lost in friction

Answer 13

Energy or force wasted due to friction.

Question 14

State the condition for reversibility of a machine

Answer 14

requires no energy losses.

Question 15

Define friction and limiting force of friction

Answer 15

*It is a force that opposes the movement of an object.
*The maximum frictional force that prevents one body from sliding over another when an external force is applied

Question 16

4 applications for centroid

Answer 16

*Indicates center of mass of a uniform solid
*Construction and engineering applications require stress and energy to ensure component stability.
*It is used to balance
-Balancing objects on a point
-balancing two people on sew-saw
*Centroids ensure balanced weight distribution and stability in machinery design.

Question 17

lami’s theorem

Answer 17

It states that if 3 forces are acting on a point in a body and it remains in equilibrium each force is directly proportional to sine of angle b/w the other 2 forces.
P/sin = Q/sin =R/sin

Question 18

define coefficient of fiction

Answer 18

Measure of surface slipperiness.

Question 19

angle of repose

Answer 19

Max slope at which loose material remains stable without sliding.

Question 20

State any two advantages and any two disadvantages of friction

Answer 20

ADV: *enables us to walk freely
* Breaks of vehicles work due to friction.
DISADV: *Mechanical energy is not conserved
*wear and tear

Question 21

State Hooke’s Law

Answer 21

within the elastic limit stress is directly proportional to strain

Question 22

State the types of axial stresses

Answer 22

Tensile stress, Volume stress and shear stress

Question 23

Define resultant force

Answer 23

Single combined force from multiple forces acting on an object.

Question 24

Distinguish between resultant and equilibrant

Answer 24

Resultant Force: Combined force from multiple forces.
Equilibrant Force: Balances out other forces

Question 25

State law of moments.

Answer 25

Moment of a force: Sum of component moments