Chp 2: Kinematics

Question 1

Define distance

Answer 1

actual path travelled by an object

Question 2

Define displacement

Answer 2

distance from a fixed point in a specified direction. It is a straight line between 2 points.

Question 3

Define velocity

Answer 3

rate of change of displacement

Question 4

Define speed

Answer 4

distance travelled per unit time

Question 5

Define acceleration

Answer 5

rate of change of velocity

Question 6

Define average speed

Answer 6

total distance travelled over total time taken.

Question 7

Define average velocity

Answer 7

total change in displacement over total time taken.

Question 8

the 4 kinematics eqn works only when:

Answer 8

1. Travel in straight line
2. Constant/uniform acceleration

Question 9

Steps to solve kinematics problems (a guide)

Answer 9

1. Define positive direction
2. Write all given data with correct sign
3. Identify unknown variables
4. Choose kinematics eqn to connect unk variable and given data
5. Solve

Question 10

Explain why acceleration can be greater than 9.81 when the ball is thrown upwards

Answer 10

Initially, the ball is thrown upwards with a certain speed. As air resistance is
not negligible, there will be an additional force acting vertically downwards
besides the gravitational force acting on the ball. Hence the resultant
acceleration that acts downwards will be greater than g.

Question 11

projectile motion

Answer 11

motion due to a uniform velocity in one direction & a uniformly accelerated motion in a perpendicular direction

Question 12

acceleration of free fall

Answer 12

acceleration of body towards the surface of earth when the only force acting in it is its weight

Question 13

Average Acceleration:

Answer 13

Average acceleration refers to the change in velocity over time taken.

Question 14

Why the path of a mass or a charged particle in a uniform electric field or gravitational
field is the same?

Answer 14

Both particles experience a uniform speed in one direction and uniform force and uniform
acceleration in a perpendicular direction. They move in a parabolic path.

Question 15

Why in the presence of air resistance, the time taken to reach the maximum height is
shorter than the time taken to return to the original position?

Answer 15

When the ball is on its way up, air resistance acts downwards, opposing the motion of the
object. The resultant force acting downwards is the sum of the air resistance and the
weight of the object. On the downward journey, air resistance acts upward, opposing the motion of the object. The resultant force acting on the object downwards is its weight
minus air resistance. Thus, the acceleration downwards is smaller in magnitude than the
deceleration in the upward journey. Since both journeys cover the same distance, the time
taken for the upward journey is shorter.

Question 16

Explain what the acceleration of a ball at its maximum height is when an object is thrown
vertically upwards.

Answer 16

At the maximum height, the object is instantaneously at rest, there will not be any drag acting on the object hence the only force acting on the object is its weight. By N2L, ma=mg, thus the acceleration of the ball at its maximum height is 9.81ms-2 downwards.

Question 17

Explain why a falling object eventually reaches constant velocity in the presence of air
resistance.

Answer 17

When an object falls, there is air resistance acting on the object upwards, since air
resistance increases with speed, as the object accelerates downwards due to gravity, the
air resistance increases. ma=mg-air resistance, as air resistance increases, the acceleration
of the object decreases until the acceleration is zero where the magnitude of the weight of
the object equals to the air resistance, the object is said to be at terminal velocity.

Question 18

Conditions for a parabolic motion in absence of air resistance.
Horizontally:
Vertically:

Answer 18

Horizontally: Horizontal component of velocity is always constant

Vertically: Vertical acceleration is always constant and downwards, with magnitude equal to 9.81ms-2

Question 19

If air resistance not negligible how does velocity vary in a projectile motion?
Horizontally:
Vertically:

Answer 19

Horizontally: Horizontal component of velocity decreases to zero

Vertically: Decreases at decreasing rate in the upward journey. Increases at a decreasing
rate in the downward journey, if the building is tall enough, the object will eventually
reach terminal velocity when the weight of the object is equal to the magnitude of air
resistance acting on the object.

Question 20

Why is the path of a ball thrown at an angle different when there is air resistance and
without air resistance?

Answer 20

With air resistance, some loss in KE is converted to work done against air resistance,
hence not all energy is converted to the GPE, hence maximum height is smaller. In the
horizontal direction, the horizontal velocity is no longer constant due to work done against
air resistance, hence the range is smaller.