3.1 Motion

Question 1

what is the definition of displacement?

Answer 1

the distance the object has moved from its starting position (vector quantity of distance)

Question 2

what is the definition of instantaneous speed?

Answer 2

the speed at a specific point in time of a journey

Question 3

what is the definition of average speed?

Answer 3

the total distance / total time taken

Question 4

what is the gradient on a displacement-time graph?

Answer 4

the object’s velocity

Question 5

what does a straight line (constant gradient) on a displacement-time graph show?

Answer 5

a constant velocity

Question 6

what is the gradient on a displacement-time graph?

Answer 6

the object’s velocity

Question 7

what does a curve indicate on a displacement-time graph show?

Answer 7

velocity is not uniform

Question 8

what does a curve of increasing positive gradient indicate on a displacement-time graph show?

Answer 8

object is accelerating (speeding up)

Question 9

what does a curve indicate on a displacement-time graph show?

Answer 9

velocity is not uniform

Question 10

what is the gradient on a velocity-time graph?

Answer 10

the object’s acceleration

Question 11

what is the area under the curve on a velocity-time graph?

Answer 11

the object’s total displacement

Question 12

what does a straight line (constant +ve gradient) indicate on a velocity-time graph show?

Answer 12

constant positive acceleration

Question 13

what does a straight line (constant -ve gradient) indicate on a velocity-time graph show?

Answer 13

constant negative acceleration

Question 14

what does a flat horizontal line indicate on a velocity-time graph?

Answer 14

constant velocity (not changing velocity)

Question 15

what does a curve indicate on a velocity-time graph?

Answer 15

tells us that the velocity change is not uniform (the acceleration isn’t uniform)

Question 16

what are the five suvat equations?

Answer 16

v = u + at
v^2 = u^2 + 2as
s = ut + 0.5at^2
s = vt - 0.5at^2
s = 0.5(u + v)t

Question 17

when can you use and apply suvat equations?

Answer 17

for an object moving with CONSTANT ACCELERATION

Question 18

outline an investigation to see how collisions affect the motion of a trolley

Answer 18

• set up an experiment with a ramp and a trolley at the top with a wall at the bottom of the ramp and a metre ruler in between ramp and wall and a video camera side on to record it
• measure the length of the trolley, L, turn on the video camera and start recording
• place trolley on start line and once the trolley has hit the wall stop recording

-to investigate the final velocities of two trolley coliding, position two trolleys on a smooth surface with a metre
ruler parallel
-measure the lengths of the two trolleys, L, and turn on video camera and record, push one trolley so hits other and stop recording

To calculate velocity:
using video analysis software, you can view frame by frame, pick a point of reference on the metre ruler and count how many frames it takes a trolley to pass that point, knowing the frame rate (no. of frames per second), the time, t, taken for the trolley to pass the point = no.of frames for trolley to pass point x 1 second/frame rate
-use L for length of trolley to do v = L/t

Question 19

outline an investigation to see how collisions with a wall and another trolley affect the motion of a trolley

Answer 19

• set up an experiment with a ramp and a trolley at the top with a wall at the bottom of the ramp and a metre ruler in between ramp and wall and a video camera side on to record it
• measure the length of the trolley, L, turn on the video camera and start recording
• place trolley on start line and once the trolley has hit the wall stop recording

-to investigate the final velocities of two trolley coliding, position two trolleys on a smooth surface with a metre
ruler parallel
-measure the lengths of the two trolleys, L, and turn on video camera and record, push one trolley so hits other and stop recording

To calculate velocity:
using video analysis software, you can view frame by frame, pick a point of reference on the metre ruler and count how many frames it takes a trolley to pass that point, knowing the frame rate (no. of frames per second), the time, t, taken for the trolley to pass the point = no.of frames for trolley to pass point x 1 second/frame rate
-use L for length of trolley to do v = L/t

Question 20

what is freefall?

Answer 20

• freefall is the acceleration of a body under the action of a gravitational field, with air resistance and buoyancy being ignored
• objects of different masses fall at the same rate under the influence of gravity
• freefall occurs when the only force acting on the object is its weight

Question 21

outline an investigation that looks at what affects the motion of a trolley on a slope

Answer 21

• to see how the distance a trolley has rolled effects it’s velocity
• set up an experiment with a trolley at the top of a ramp with a light gate at the bottom which is also connected to a data logger
• measure the length of the trolley, the angle of the ramp (theta) and the distance from the chosen start line to light gate, d (mark start line on ramp)
• place the trolley on the line and let go (meaning u = 0), the data logger will record the time taken for the trolley to pass through the light gate and calculate the velocity at this point
• change the starting position to vary d
• repeat to gain average velocities and to reduce error and record results
• use s = 0.5(u + v)t

Question 22

what is the relationship between acceleration, force and mass?

Answer 22

acceleration is directly proportional to the force acting on it but inversely proportional to its mass (f = ma)

Question 23

outline an investigation to determine g using a trapdoor and an electromagnet

Answer 23

• set up a circuit with an electromagnet supporting a steel ball, a switch, a timer and a trapdoor directly underneath the ball bearing
• when the current is switched off, the ball begins to fall and and the timer simultaneously starts
• once it hits the trapdoor the timer is stopped
• the distance, s, between the bottom of the ball bearing and the trapdoor is measured using a ruler and the time, t, is taken from timer readings
• repeat to get an average for t
• u = 0 because the ball starts from rest therefore can use suvat —> s = 0.5at^2, rearrange and solve for g
• alternatively a graph can be plotted of s (y axis) against t^2 (x axis) so the gradient = 0.5g (as y intercept is 0)

(note if the distance is too large air resistance might have a noticeable effect on the speed, also the height can causes uncertainty, ensure accurate measurement)

Question 24

outline an investigation to determine g using lightgates

Answer 24

• use lightgates and a data logger to measure the time e taken fro a piece of card to travel through the light gate as it falls
• blu-tack can be added to the corners of the card to stabilise it better
• the data logger can record the velocity or you can use a timer and work out the average velocity of card is given by L/t where L is the length of the card and t is the transit time recorded by the timer for the card to travel through the light gate
• use a ruler to measure the vertical height of the card above the light gate, s
• hold the card vertically above the lightgate before releasing it
• use suvat, u = 0 because initially from rest so use —> v^2 = 2as, rearrange and solve for g
• varying the height allows a graph to be plotted, v^2 on y axis and s on x axis, gradient = 2g

Question 25

what is braking distance?

Answer 25

the distance the vehicle travels after the brakes have been applied until it comes to a stop

Question 26

what is thinking distance?

Answer 26

the distance the vehicle travels during the driver’s reaction time (speed x reaction time)

Question 27

what is stopping distance?

Answer 27

stopping distance = thinking distance + breaking distance (total distance to stop)

Question 28

what factors can affect thinking distance?

Answer 28

• higher speed
• tiredness
• alcohol and drugs
• distractions (music etc.)
• age of driver

Question 29

what factors can affect braking distance?

Answer 29

• higher speed
• poor road conditions (icy or wet)
• poor condition of tyres
• poor condition of brakes
• mass of car (more luggage or people etc.)

Question 30

why is the relationship between speed and thinking distance linear while the relationship between speed and braking distance not linear?

Answer 30

• thinking distance relationship is linear because reaction time is fixed and therefore goes up in multiples
• braking distance relationship isn’t linear because at higher speeds it takes a longer amount of time to slow down and come to a stop

Question 31

when answering projectile motion questions what must your remember?

Answer 31

• you have to think of horizontal and vertical motion SEPARATELY
• a projectile has vertical and horizontal components INDEPENDENT of one another

Question 32

why does a projectile follow a curved/parabolic path?

Answer 32

projectiles follow a horizontal path because the horizontal velocity remains constant, while the vertical velocity is affected by the perpendicular acceleration due to gravity

Question 33

when answering projectile motion questions with SUVAT what is important to remember?

Answer 33

• the horizontal component of velocity is always CONSTANT and therefore you can use speed = distance/time
• the vertical component is affected by constant acceleration due to gravity and therefore you must use SUVAT
• time is common to both of them

Question 34

how do you resolve a velocity vector into its horizontal and vertical components?

Answer 34

horizontal component = Vcosθ

vertical component = Vsinθ