Projectile Motion Flashcards
What is a projectile?
Any object acted upon only by the force of gravity.
State the three key principles apply to all projectiles.
- Acceleration is always equal to g and is always downwards. Therefore only the vertical motion of the object is affected by acceleration
- Horizontal velocity is a constant as object does not have a horizontal component
- Motions in the horizontal and vertices directions are independent to each other
What are the equations used for vertices projection?
v= u-gt
y=ut- 1/2 gt^2
Explain the horizontal projection of a stone thrown from a cliff top.
The stone follows a curved path downwards.
Explain what would happen if the stone thrown off the cliffs’ initial projection is horizontal.
- It’s path through the air becomes steeper and steeper as it drops
- The faster its projected, the further away it will fall to the bottom
- The time taken for it to fall into the sea does not depend on how fast it is projected
Suppose two balls are released at the same time. One thrown vertically and the other is projected horizontally. Which hits the floor first? Explain your answer.
They both hit the floor simultaneously as they are both pulled to the ground by the for of gravity which gives them the same downward acceleration. This downward acceleration does not affect the horizontal motion of the ball only the vertical.
Describe the practical used to investigate the horizontal projection.
Use a stroboscopic and camera with a slow shutter to record the motion of the projectile. Ball A will be released from rest and topped vertically while ball B was given an initial horizontal projection so it follows a curved path.
The stroboscopic flashes at a constant rate so the images of both balls are recorded at the same time.
Describe and explain the horizontal position of the balls when investigating the horizontal projection
The horizontal projection of the ball given an initial horizontal projection changes by equal distances between successive flashes. This shows that the horizontal component of Bs velocity is constant.
Explain the vertical position of the balls in the horizontal projection practical
A and B changes at the same rate. At any instant, A is the same level as B. This shows that A and B have the same vertical component of velocity at any instant
Describe how to find the projectile path of a ball projected horizontally
The horizontal component of its displacement,
x= Ut
(Because it moves horizontally at a constant speed)
The vertical component of its displacement,
y=1/2gt^2
(Because it has no vertical component of its initial velocity)
It’s velocity has a horizontal component v(x)= U and a vertical component v(y)= =gt
Describe how to find the projectile path of a ball projected horizontally
The horizontal component of its displacement,
x= Ut
(Because it moves horizontally at a constant speed)
The vertical component of its displacement,
y=1/2gt^2
(Because it has no vertical component of its initial velocity)
It’s velocity has a horizontal component v(x)= U and a vertical component v(y)= =gt
What is air resistance?
A drag force
Explain how air resistance acts on an object?
Acts in the opposite direction from the direction of motion and it increases as the speed increases.
It has a horizontal component which reduces both the horizontal speed of the projectile and its range.
It reduces the max height of the projectile if its initial direction is above the horizontal and makes its descent steeper than its ascent.
How to find the horizontal and vertical displacement without gravity
Horizontal, x= Ut cos th
Vertical, y= Ut sin th
Considering gravity, what would the displacement of a projectile motion (horizontal and vertical) be?
Vertical position: 1/2 gt^2 lower
Vertical component of velocity= change by -gt from its initial value sin th
Y= Ut sin th - 1/2gt^2
Vy= Usin th-gt
