Motion

Question 1

What is displacement?

Answer 1

Distance in a given direction

Question 2

What is speed?

Answer 2

Change of distance per unit time

Question 3

What is velocity?

Answer 3

Change in displacement per unit time. or speed in a given direction.

Question 4

Between speed, velocity and displacement, distance which are vectors or scalar?

Answer 4

Speed and distance are scalar quantities. Velocity and displacement are vector quantities.

Question 5

What is the unit for speed and velocity?

Answer 5

ms-1

Question 6

For example, a car travelling at a speed of 30 ms
−1 on a motorway travels a distance of
30 m every second.
How many meter in every minute?
What about in 1 hour?
Convert 30 ms
−1
to kmh−1?

Answer 6

1800 m every minute.

In 1 hour, the car would therefore travel a distance of 108000m or 108km

30 ms
−1 = 108 kmh−1
.

Question 7

What is the equation for speed?

Answer 7

For an object which travels distance s in time t at constant speed.
Speed 𝑣 = s/t
Distance travelled 𝑠 = 𝑣t

Question 8

What is the equation for an object moving at constant speed on a circle of radius r,

Answer 8

𝑣 =
2𝜋𝑟/T

where T is the time to move round once and 2𝜋𝑟 is the circumference of the circle

Question 9

What is the equation for average speed?

Answer 9

𝑣 = ∆𝑠/∆t

Question 10

What is the graph of an object moving at constant speed on a distance-time graph?

Answer 10

a straight line
with a constant gradient.

Question 11

What is the graph of an object moving at changing speed on a distance-time graph?

Answer 11

The gradient of the graph changes so the speed of the object is calculated as distance travelled/time taken

Question 12

How is speed calculated on a distance-tie graph?

Answer 12

The gradient of the line i.e distance travelled/ time taken

Question 13

Can an object moving at constant velocity move at the same speed when changing direction?

Answer 13

An object moving at constant velocity moves at the same speed without changing
its direction of motion.
If an object changes its direction of motion or its speed or both, its velocity changes.
For example, the velocity of an object moving on a circular path at constant speed
changes continuously because its direction of motion changes continuously

Question 14

What is Acceleration?

Answer 14

Change of velocity per unit time (ms-2). It is a vector

Question 15

What is uniform acceleration?

Answer 15

The velocity of an object moving along a straight line changes at a constant rate. This is when acceleration is constant.

Question 16

What is is the equation to calculate acceleration

Answer 16

𝑎 = (𝑣 − 𝑢)/t

Question 17

What is non-uniform acceleration?

Answer 17

the direction of motion of an object changes, or its speed changes, at a
varying rate.

Question 18

What is the gradient of a velocity-time graph used to calculate?

Answer 18

Non uniform acceleration.

Question 19

What are the 4 suvat equations?

Answer 19

1. 𝒗 = 𝒖 + 𝒂𝒕
2. 𝒔 = ((𝒖+𝒗) 𝒕)/2
3. 𝒔 = 𝒖𝒕 + 0.5𝒂𝒕^𝟐
4. 𝒗^𝟐= 𝒖^𝟐 + 𝟐𝒂s

Question 20

How can you find displacement using a velocity-time graph?

Answer 20

1. If at constant velocity: The area under the line between the start and time t since displacement = v x t

2: If at constant acceleration: since 𝒔 = ((𝒖+𝒗) 𝒕)/2 then displacement is the area under the line between start and time t, calculated as a triangle

3. Changing acceleration: the area under the line where v represent the velocity at time t and v + 𝛿v represent the velocity a short time
   later at t + 𝛿t . (𝛿 is pronounced ‘delta’.)
   Because the velocity change 𝛿v is small compared with the velocity v, the displacement
   𝛿s in the short time interval 𝛿t is v𝛿𝑡.
   This is represented on the graph by the area of the shaded strip under the line, which
   has a base corresponding to 𝛿t and a height corresponding to v. In other words,𝛿𝑠= v𝛿t
   is represented by the area of this strip

Question 21

What is the acceleration of freefall?

Answer 21

The acceleration of freefall is the constant acceleration of a free falling object denoted by g. It is equal to 9.81ms^-2

Question 21

Can suvat be used in freefall situations?

Answer 21

Only when air resistance is negligible

Question 21

How should freefall values be entered into suvat equations?

Answer 21

+ for items thrown upwards, - for falling downwards.

Question 21

Describe a Displacement time graph
for on object projected upwards

Answer 21

• Immediately after leaving the thrower’s hand, the velocity is
  positive and large, so the gradient is positive and large.
• As the ball rises, its velocity decreases so the gradient decreases.
• At maximum height. its velocity is zero, so the gradient is zero.
• As the ball descends, its velocity becomes increasingly negative,
  corresponding to increasing speed in a downward direction.
  So the gradient becomes increasingly negative It looks like an upside down U

Question 22

A coin was released at rest at the top of a well. It took 1.6s to hit the bottom of the well. Calculate; (g = 9.8 ms −2) a) the distance fallen by the coin, b) its speed just before impact.

Answer 22

a= -12.5m b =-15.7

Question 23

What is the gradient of a Displacement-time graph for an object projected upwards

Answer 23

Velocity

Question 24

What is the gradient of a Distance-time graph for an object projected upwards

Answer 24

Speed

Question 24

Distance-time graph for an object projected upwards

Answer 24

The gradient of this line represents the speed. From projection to maximum height, the shape is exactly the same as the previous slide. After maximum height, the distance continues to increase so the line curves up. It is half an upside down u and then the other half turn upwards like a regular U

Question 25

The difference between a speed-time graph and a velocity-time graph

Answer 25

The object’s velocity decreases from its initial positive (upwards) value to zero at maximum height and then increases in the negative (downwards) direction as it falls.Speed mainly increases and decreases

Question 26

What is the gradient of a velocity time graph?

Answer 26

The gradient of the line represents the object's acceleration. This is constant and negative, equal to the acceleration of free fall, g. The acceleration of the object is the same when it descends as when it ascends so the gradient of the line is always equal to -9.8 ms −2

Question 27

What does the area under the line represent on a velocity time graph?

Answer 27

The area under the line represents the displacement of the object from its starting position. The area between the positive section of the line and the time axis represents the displacement during the ascent. The area under the negative section of the line and the time axis represents the displacement during the descent. Taking the area for a as positive and the area for b as negative, the total area is therefore zero. This corresponds to zero for the total displacement.

Question 28

What does a velocity time graph of an object thrown and caught look like?

Answer 28

It looks like this \, The object’s velocity decreases from its initial positive (upwards) value to zero at maximum height and then increases in the negative (downwards) direction as it falls.

Question 29

A ball released from a height of 1.20 m above a concrete floor rebounds to a height of 0.82m. a) Calculate i its time of descent, ii the speed of the ball immediately before it hits the floor. b) Calculate i the speed of the ball immediately after it leaves the floor, ii its time of ascent. c) Sketch a velocity-time graph for the ball. Assume the contact time is negligible compared with the time of descent or ascent and that positive velocity is upwards

Answer 29

a. t= 0.49, ii. -4.8ms-1 b u = 4.0ms-1 ii. t = 0.41s

Question 30

A space vehicle moving towards a docking station at a velocity of 2.5 ms −1 is 26 m from the docking station when its reverse thrust motors are switched on to slow it down and stop it when it reaches the station. The vehicle decelerates uniformly until it comes to rest at the docking station when its motors are switched off. Calculate a its deceleration, b how long it takes to stop

Answer 30

initial velocity u = +2.5 ms −1 , final velocity v = 0, displacements= +26 m. a. -0.12ms-2 b. 21s

Question 31

What is the link between acceleration in two - stage problems

Answer 31

The acceleration in each stage is not the same. The link between the two stages is that the velocity at the end of the first stage is the same as the velocity at the start of the second stage. Consider an object released from rest, falling, and then hitting a bed of sand. The motion is in two stages: ➢ falling motion due to gravity: acceleration = g (downwards) ➢ deceleration in the sand: initial velocity = velocity of the object just before impact

Question 32

a ball is released from a height of 0.85 m above a bed of sand and creates an impression in the sand of a depth 0.025 m. Calculate the speed of impact.

Answer 32

a. v=-4.1ms-1 stage 2= decellerarion = 336ms-2

Question 33

What is a projectile?

Answer 33

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

Question 34

What are the principles of a projectile?

Answer 34

* The acceleration of the object is always equal to g and is always downwards - g is the only factor affecting vertical motion * The horizontal velocity of the object is constant because the acceleration of the object does not have a horizontal component. * Horizontal and vertical velocity are independent of each other

Question 35

what are the equations of displacement y and velocity v after time t during vertical projection?

Answer 35

𝒗 = 𝒖 − 𝒈𝒕 𝒚 = 𝒖𝒕 − 1/2𝒈𝒕^2

Question 36

Describe the horizontal projection of A stone thrown from a cliff top follows a curved path downwards before it hits the water

Answer 36

If its initial projection is horizontal: * its path through the air becomes steeper and steeper as it drops * the faster it is projected, the further away it will fall into the sea * the time taken for it to fall into the sea does not depend on how fast it is projected.

Question 37

Suppose two balls are released at the same time above a level floor such that one ball drops vertically and the other is projected horizontally. Which one hits the floor first? Why?

Answer 37

They both hit the floor simultaneously. Why? They are both pulled to the ground by the force of gravity, which gives each ball a downward acceleration g. The ball that is projected horizontally experiences the same downward acceleration as the other ball. This downward acceleration does not affect the horizontal motion of the ball projected horizontally- only the vertical motion is affected.

Question 38

Describe the graph of a projectile path of a ball projected horizontally

Answer 38

An object projected horizontally falls in an arc towards the ground. If its initial velocity is 𝑼, then at time t after projection: 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). lts velocity has a horizontal component 𝑣𝑥 = 𝑈, and a vertical component 𝑣𝑦 = −𝑔𝑡. Note that, at time t, the speed = (𝑣𝑥^2+ 𝑣𝑦^2)1/2

Question 39

An object is projected horizontally at a speed of 15 ms−1from the top of a tower of height 35.0m. Calculate: a) how long it takes to fall to the ground b) how far it travels horizontally c) its speed just before it hits the ground

Answer 39

a. t = 2.67 b x = 40m c. v = 30.2ms-1

Question 40

What are the equations for vertical projection?

Answer 40

v = u -gt y = ut -1/2gt^2

Question 41

What is the measurement for gravitational field strength?

Answer 41

9.81 N kg-1

Question 42

What is Newton's Second Law of motion?

Answer 42

Acceleration of an object is proportional to the resultant force acting on it. The rate of change of momentum of an object is proportional to the resultant force on it. The resultant force is proportional to the change of momentum per second

Question 43

What is Newton's third law?

Answer 43

When two objects interact they exert equal and opposite forces on each other.

Question 44

How are projectiles calculated?

Answer 44

Since horizontal and vertical motion is separate, we calculate vertical motion using suvat and horizontal motion with = speed=d/t