On the Move

Question 1

Name the 5 SUVAT equations

Answer 1

s = [ (u+v)/2 ]t
v = u + at
s = ut + ½at²
s = vt - ½at²
v² = u² + 2as

Question 2

Explain why a projectile will only experience an acceleration in the vertical direction

Answer 2

Vertical and horizontal motion are completely independent

The force of gravity only acts vertically on an object

Question 3

Define displacement

Answer 3

The distance in a given direction

Question 4

Define speed

Answer 4

The change of distance per unit time

Question 5

Define velocity

Answer 5

The change of displacement per unit time

speed in a given direction

Question 6

Give the shape of the line for a graph of distance vs. time for an object at constant speed

Answer 6

A straight line (linear)

Question 7

Describe how the speed of an object can be calculated for a graph of distance against time where the line is:

i) linear
ii) non-linear

Answer 7

i) speed = gradient
ii) speed at a time = gradient of curve at that time, which can be measured by drawing a tangent to the curve and measuring the gradient of the tangent

Question 8

Define acceleration

Answer 8

The change in velocity per unit time`

Question 9

Give the equation for uniform acceleration, given the object’s initial and final velocity

Answer 9

a = (v - u) / t

Question 10

What does the gradient of the line represent for a velocity vs. time graph?

Answer 10

The acceleration

Question 11

What does the area under the line represent for a velocity vs. time graph?

Answer 11

The displacement

Question 12

Describe a method to investigate the acceleration due to gravity of an object in free fall

Answer 12

Setting up a stroboscope at a known flash rate and a camera and dropping a ball in front of a metre rule and a dark background. The metre rule acts as a scale, so the displacement of the ball between each image (when the stroboscope flashes) can be measured

Question 13

Describe the difference between a displacement vs. time graph and a distance vs. time graph for a ball thrown vertically upwards

Answer 13

Since displacement is distance in a given direction, a ball thrown into the air will finish with 0 displacement, but a distance of twice the maximum height.
Therefore overtime, the displacement will increase, hit a maximum and decrease, whereas the distance will increase to the maximum height (where it levels off) and then increase yet again

Question 14

Define a projectile

Answer 14

A projectile is any object acted upon by the force of gravity

Question 15

What 3 key principles apply to all projectiles?

Answer 15

1) The acceleration of the object is always equal to g and is always downwards
2) The horizontal velocity of the object is constant because the acceleration of the object doesn’t have a horizontal component
3) The motion in the horizontal and vertical directions are independent of each other

Question 16

For an object projected horizontally, give 3 statements that will always be true

Answer 16

1) Its path through the air becomes steeper as it drops
2) The faster it is projected, the further away it will land
3) The time taken for it to land doesn’t depend on how fast it is projected

Question 17

Describe an experiment to investigate horizontal projection and explain its results

Answer 17

• Setting up a stroboscope and camera with a slow shutter. Drop one ball at the same time as a second ball being given horizontal projection.
• The horizontal position of the 2nd ball changes by equal distances between successive flashes because the horizontal component of the ball’s velocity is constant
• The vertical position of the 1st and 2nd ball changes at the same rate, because they both have the same vertical component of velocity at any instant

Question 18

Give an equation for the horizontal component of an object projected horizontally

Answer 18

Displacement x = ut

Question 19

Give an equation for the vertical component of an object projected horizontally

Answer 19

Displacement y = ½gt²

Question 20

Give the conditions required for the motion of an object to be described as projectile-like motion

Answer 20

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

Question 21

Give 2 examples of objects moving with projectile-like motion and explain why

Answer 21

1) The path of a ball rolling across an inclined board will be a projectile path. Its path is parabolic because the object is subjected to constant acceleration down the board but its initial velocity is across the board
2) The path of a beam of electrons directed between two oppositely charged plates will be parabolic because each electron is acted on by a constant force towards the positive plate (due to charge) but its motion parallel to the plates is at 0 acceleration

Question 22

Describe a mathematical method to find the speed of an object with horizontal projection when given the components of its velocity in the horizontal and vertical direction

Answer 22

Treat the velocities as sides of a triangle, and solve to find the hypotenuse
e.g. if the velocity of the horizontal component = vₓ
and the velocity of the vertical component = vᵧ
Then the speed at time t is given by
√(vₓ² + vᵧ²)

Question 23

For an object in 0g, projected into the air at speed U in the direction at angle θ, give the horizontal and vertical components for its displacement at time t

Answer 23

Horizontal component x = Ut cosθ

Vertical component y = Ut sinθ

Question 24

How much higher would an object projected in 0g be than when acted upon by gravity if its initial speed was U in the direction at angle θ?

Answer 24

It would be ½gt² higher