7.8 Projectile motion 2

Question 1

Any form of motion where an object experiences a constant acceleration in a different direction to its velocity will be like _____ _____

Answer 1

Projectile motion

Question 2

Example of projectile-like motion - ball rolling across an inclined board

Answer 2

The object is projected across the top of the board from the side, its path curves down the board and is parabolic. This is because the object is subjected to constant acceleration acting down the board and it initial velocity is across the board

Question 3

Example of projectile motion - beam of electrons directed between two oppositely charged parallel plates

Answer 3

Parabolic
Each electron in the beam is acted on by a constant force towards the positive plate because the charge of an electron is negative. Therefore, each electron experiences a constant aacceleration towards the positive plate. Its path is parabolic because its motion parallel to the plates is at ZERO accleration whereas its motion perpendicular to the plates is at constant (non-zero) acceleration

Question 4

What force does a projectile experience

Answer 4

A drag force/air resistance

Question 5

What is the drag force experienced by projectiles caused by

Answer 5

Friction between the layers of air near the projectile’s surface where the air flows over the surface

Question 6

The drag force:

Answer 6

Acts in the opposite direction to the direction of motion of the projectile, and it increases as the projectile’s speed increases
Has a horizontal component that reduces both the horizontal speed of the projectile and its range
Reduces the maximum height of the projectile if its initial direction is above the horizontal and makes its descent steeper than its ascent

Question 7

Why is the shape of the projectile important

Answer 7

It affects the drag force and may also cause a lift force in the same way as the cross-sectional shape of an aircraft wing creates a lift force

Question 8

What causes a lift force

Answer 8

Certain shapes which cause the air to flow faster over the top of the object than underneath it. Therefore, the pressure of the air on the top is less than that on the bottom surface, this pressure difference causes a lift force

Question 9

Displacement at time after projection of an object without gravity or air resistance acting on it

Answer 9

Horizontal component
x=Utcosθ
Vertical component
y=Utsinθ

THEREFORE:
y=Utsinθ - 1/2gt^2
vy=Usinθ - gt