Topic 1A - Projectile Motion

Question 1

What equation can be used to calculate time of flight when object is launched horizontally?

Answer 1

s = ut + 1/2 at(2)

distance = (initial velocity)(time) + 1/2(acceleration)(time of flight squared)

Question 2

What equation can be used to calculate time of flight for uni-level projectiles?

Answer 2

s = ut + 1/2 at(2)

distance = (initial velocity)(time) + 1/2(acceleration)(time of flight squared)

Question 3

For uni-level projectiles, what angle produces maximum range?

Answer 3

45 degrees

Question 4

What launch angles will produce the same range?

Answer 4

Launch angles that add up to 90 degrees will produces the same range.

e.g. - projectile launched at 80 degrees and projectile launched at 10 degrees will produce same range

Question 5

increase launch height has what impact on launch angle that produces maximum range

Answer 5

As launch height increases the angle that produces maximum range decreases

Question 6

What is drag force?

Answer 6

When moving through a medium a body experiences a drag force. It is mostly commonly known as air resistance and is always in the opposite direction to that of motion..

Question 7

What impact does speed have on air resistance?

Why?

Answer 7

Increase in speed results in increased air resistance as more air particles collide with the body per unit of time

Question 8

What impact does cross-sectional area have on air resistance?
Why?

Answer 8

Increase in cross-sectional area results in increased air resistance as more air particles collide with the body per unit of time

Question 9

What impact does density have on air resistance?

Why?

Answer 9

Increase in density increases air resistance experienced as there are more particles per unit of air.
TF, increased contact with body - more particle colliding with body per unit of time.

Question 10

What is terminal velocity and when does it occur?

Answer 10

Terminal velocity occurs when the net force on a body is zero. The acceleration due to gravity is cancelled out by the air resistance or drag force.

Question 11

Explain the application of terminal velocity for a skydiver (both without parachute and with)

Answer 11

Initially, the acceleration due to gravity is greater than the drag force as the diver is moving slowly.
As the diver increases in speed the air resistance increases whilst the acceleration remains the same.
TF, drag = acceleration a some point and terminal velocity is reached.

Parachute is released
Increase surface area TF increase drag force
TF, drag force is greater than acceleration and the diver is no longer travelling at terminal velocity
As diver slows down, the drag force decreases
TF, acceleration = drag force again although terminal velocity will be slower

Question 12

Explain terminal velocity in terms of racing cars

Answer 12

There will be time at which the thrust of the engine is equal to the magnitude of the air resistance.
TF, racecar will reach a terminal velocity.

Question 13

Draw a diagram showing the effect of air resistance on the path of a projectile

Answer 13

Less height
Smaller range
sharp drop at the end

Question 14

Explain the affect of air resistance on a projectile’s time of flight

Answer 14

air resistance will cause a deceleration of both the horizontal and vertical components of the object’s velocity.
TF, the max height and range will decrease.
AR decreases the time taken to reach max height but increases the time taken to fall as it acts in the opposite direction to motion of the particle.
TF, no significant change in flight time