Kinematics

Question 1

Define displacement

Answer 1

Displacement of an object is its distance from a fixed point in a specific direction

Question 2

Define speed

Answer 2

Speed is defined as the total distance travelled over the total time taken.

Question 3

Define velocity

Answer 3

The velocity of a body is defined as the rate of change of its displacement

Question 4

Define acceleration

Answer 4

The acceleration of a body is defined as the rate of change of its velocity

Question 5

Horizontal Motion equations

Answer 5

s=ut
v=u

Question 6

Vertical Motion equations

Answer 6

s = ut + (at^2)/2 (When v not given)
v = u + at (When s not given)
v^2 = u^2 + 2as (When t not given)

Question 7

Why do equations of motion not apply in the presence of air resistance?
State and explain the actual motion in the presence of air resistance

Answer 7

In the presence of air resistance, the body experiences a force in the direction opposite to its motion. As the speed of the projectile changes, air resistance acting on it also changes.

As it travels up, both drag force and weight act downwards and thus the net downward force is larger. By Newton’s Second Law, the downward acceleration is therefore larger than gravitational field strength (9.81m/s^2). This causes the body to reach a smaller altitude and to reach maximum height sooner. Since there is air resistance acting in the horizontal direction as well, the horizontal velocity is reduced and the range is now smaller.