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 is the gradient on a velocity-time graph?

Answer 9

the object’s acceleration

Question 10

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

Answer 10

the object’s total displacement

Question 11

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

Answer 11

constant positive acceleration

Question 12

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

Answer 12

constant negative acceleration

Question 13

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

Answer 13

constant velocity (not changing velocity)

Question 14

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

Answer 14

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

Question 15

what are the five suvat equations?

Answer 15

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 16

when can you use and apply suvat equations?

Answer 16

for an object moving with CONSTANT ACCELERATION

Question 17

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

Answer 17

• 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 18

outline an investigation to see how collisions with a wall and another trolley 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

what is freefall?

Answer 19

• 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 20

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

Answer 20

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 21

what is the relationship between acceleration, force and mass?

Answer 21

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

Question 22

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

Answer 22

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 23

outline an investigation to determine g using lightgates

Answer 23

use lightgates and a data logger to measure the time e taken from 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 24

what is braking distance?

Answer 24

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

Question 25

what is thinking distance?

Answer 25

the distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake

thinking distance = speed x reaction time

Question 26

what is stopping distance?

Answer 26

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

Question 27

what factors can affect thinking distance?

Answer 27

higher speed

tiredness

alcohol and drugs

distractions (music etc.)

age of driver

Question 28

what factors can affect braking distance?

Answer 28

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 29

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

Answer 29

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 30

when answering projectile motion questions what must your remember?

Answer 30

you have to think of horizontal and vertical motion SEPARATELY

a projectile has vertical and horizontal components INDEPENDENT of one another

Question 31

why does a projectile follow a curved/parabolic path?

Answer 31

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 32

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

Answer 32

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 33

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

Answer 33

horizontal component = Vcosθ

vertical component = Vsinθ

Question 34

Thinking distance formula is

Answer 34

Speed x reaction time