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

Answer 6

velocity is not uniform

Question 7

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

Answer 7

object is accelerating (speeding up)

Question 8

what is the gradient on a velocity-time graph?

Answer 8

the object’s acceleration

Question 9

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

Answer 9

the object’s total displacement

Question 10

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

Answer 10

constant positive acceleration

Question 11

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

Answer 11

constant negative acceleration

Question 12

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

Answer 12

constant velocity (not changing velocity)

Question 13

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

Answer 13

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

Question 14

what are the five suvat equations?

Answer 14

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 15

when can you use and apply suvat equations?

Answer 15

for an object moving with CONSTANT ACCELERATION

Question 16

what is freefall?

Answer 16

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 17

what is the relationship between acceleration, force and mass?

Answer 17

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

Question 18

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

Answer 18

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 19

outline an investigation to determine g using lightgates

Answer 19

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, shold 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 20

what is braking distance?

Answer 20

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

Question 21

what is thinking distance?

Answer 21

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

Question 22

what factors can affect thinking distance?

Answer 22

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

Question 23

what factors can affect braking distance?

Answer 23

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 24

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

Answer 24

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 25

when answering projectile motion questions what must your remember?

Answer 25

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

Question 26

why does a projectile follow a curved/parabolic path?

Answer 26

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 27

what is stopping distance?

Answer 27

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