Dynamics

Question 1

Define mass of a body

Answer 1

The measure of its resistance to change it’s state of motion

Question 2

Define momentum of a body

Answer 2

The product of it’s mass and it’s velocity

Question 3

Force acting on a body is defined as

Answer 3

the rate of change of momentum of the body

Question 4

Formula for force

Answer 4

F = (dP)/(dt)

Question 5

Impulse is

Answer 5

The product of the force acting on a body and the time of impact on the force

Ft

Question 6

N1L

Answer 6

a body will continue to be at rest or continue to move at constant velocity unless a resultant external force acts on it

Question 7

N2L

Answer 7

The rate of change of momentum of a body is proportional to the resultant external force exerted on it and the change in momentum is in the direction of the force.

Question 8

N3L

Answer 8

When body A exerts a force on body B, body B exerts an equal and opposite force on body A.

Question 9

Principle of conversation of linear momentum

Answer 9

The total momentum of the bodies in the system remains constant if there is no resultant external forces acting on it

Question 10

Formula for principle of conservation of linear momentum

Answer 10

M1U1 + M2U2 = M1V1 + M2V2

Question 11

Formula for elastic collision

Answer 11

U1 + U2 = V2 - V1

Question 12

For KE to be fully conserved (formula)

Answer 12

½m1(u1)^2 + ½m2(u2)^2 = ½m1(v1)^2 + ½m2(v2)^2

Question 13

Derive impulse from the equation of momentum/

Answer 13

p = mv
F = dp/dt
Impulse = Ft

Question 14

Derive U1 - U2 = V2 - V1

Answer 14

For momentum to be conserved, m1u1 + m2u2 = m1v1 + m2v2 - (1)

For kinetic energy to be fully conserved, ½m1u1² + ½m2u2² = ½m1v1² + ½m2v2² - (2)

From (1) - m1(u1-v1) = m2(u2-v2) - (3)
From (2) - m1(u1²-v1²) = m2(u2²-v2²) - (4)

(4)/(3):
u1+v1= u2+v2
u1-u2 = v2-v1

Question 15

State what is meant by an inelastic collision between 2 objects by reference to the speed of the objects.

Answer 15

Relative speed of approach before collision ≠ relative speed of separation after collision.

Question 16

State what is meant by an inelastic collision between 2 objects by reference to the energy of the objects.

Answer 16

Total initial KE ≠ total final KE and is transferred to other forms of energy.

(NOT “energy is conserved”)

Question 17

Why does a falling object reach constant velocity?

Answer 17

Air resistance, which acts opposite to the object’s motion, increases as speed of object increases.
Resultant force on the object which is the difference in it’s weight and air resistance, would decrease as the object falls.
Eventually, when magnitude of air resistance is equal to the object’s weight, resultant force = 0 and by N2L, acceleration = 0 and object reaches constant velocity.