motion

Question 1

how can the average speed of an object be calculated

Answer 1

distance travelled/time taken

Question 2

what are distance time graphs used to represent

Answer 2

the motion of objects

Question 3

what is the gradient of a distance time graph

Answer 3

the speed of the object

Question 4

how you represent an object moving at a constant speed, stationary on a distance time graph

Answer 4

constant - straight, sloping line
stationary - horizontal straight line

Question 5

what is instantaneous speed

Answer 5

the speed of the car over a very short interval of time
found by drawing tangent to distance time graph at that time and then determining the gradient - the greater the gradient the greater the instantaneous speed

Question 6

what is a displacement quantity

Answer 6

has both direction and magnitude

Question 7

what is a scalar quantity

Answer 7

only has magnitude

Question 8

what are examples of vector quantities

Answer 8

momentum, force, displacement, velocity, weight, acceleration

Question 9

what are examples of a scalar quantities

Answer 9

mass, energy, power, time, temp, speed, distance, current

Question 10

how would you work out the average velocity of an object

Answer 10

change in displacement/time taken

Question 11

what do displacement time graphs represent

Answer 11

the motion of an object`

Question 12

what is the gradient of a displacement time graph

Answer 12

the velocity

Question 13

what is aceleration

Answer 13

the rate of change of velocity
change in velocity/time

Question 14

what is the unit of acceleration

Answer 14

ms^-2

Question 15

is aceleration a vector or scalar quanitty

Answer 15

vector

Question 16

how do you calculate aceleration

Answer 16

change in velocity/change in time
from a velocity time graph

Question 17

how do you work out acceleration from a velocity time graph

Answer 17

the gradient

Question 18

what is the area under a velocity time graph

Answer 18

the displacement

Question 19

what are the suvat equation

Answer 19

v=u+at
s=ut+1/2at^2
s=1/2(u+v)t
v^2=u^2+2as

Question 20

how do you derive the equation v=u+at

Answer 20

from velocity time graph
gradient - a=v-u/t
can be rearranged to give
v=u+at

Question 21

how do you derive the equation s=ut+1/2at^2

Answer 21

area under velocity time graph equals displacement s
the rectangle area = u x t
the triangle area = 1/2 x (v-u) x t
from equation v-u = at substitute this into the expression for the area of the triangle get 1/2 x at x t
with ut for the area of the rectangle this ives the total area s
s=ut+1/2at^2

Question 22

how do you derive the equation s=1/2(u+v)t

Answer 22

treat the area under the graph as the area of a trapezium
s=(u+v)t/2

Question 23

how do you derive the equation v^2=u^2+2as

Answer 23

v=u+at
t=(v-u)/a
equation substituted into s=1/2(u+v)t to give s=1/2(u+v) x (v-u)/a
rearranging gives (v+u)(v-u) = 2as
v^2-u^2 = 2as
v^2=u^2+2as

Question 24

what is the stopping distance

Answer 24

the total distance travelled from when the driver first sees a reason to stop to when the vehicle stops
thinking distance + braking distance

Question 25

what is the thinking distance

Answer 25

the distance travelled between the moment when the hazard is spotted to the moment the driver applies the break proportionate to the initial speed of the car

Question 26

what is the braking distance

Answer 26

the distance travelled from the time the break is applied until the vehicle stops proportionate to the square of the initial speed of the car u^2

Question 27

how can the thinking distance be calculated

Answer 27

multiplying the initial speed of the car by the reaction time of the driver

Question 28

what is the thinking distance affected by

Answer 28

the initial speed of the car factors that affect the drivers reaction time - tiredness, being under the influence of alchol and drugs, other distractions

Question 29

what is the braking distance increased by

Answer 29

poor road conditions - icy, wet car condition - poor brakes, heavy load

Question 30

what happens when an object is in free fall

Answer 30

it is accelerating under gravity with no other forces acting on it acceleration of free fall denoted by the label g

Question 31

how do you determine g

Answer 31

- drop a ball over a known distance and time its descent - happens very quickly - electromagnet and a trap door - electromagnet holds a small stell ball above a trapdoor, when the current is switched off a timer is triggered and the electromagnet demagnetises and the ball falls, when it hits the trapdoor the electrical contact is broken and the time stops, the value for g is calculated from the height if the fall and the time taken (suvat), the electromagnet and trapdoor introduce tiny delays into the timing - light gates - two light beams above one another with detectors connected to a timer, when the ball falls through the first beam it interrupts the light and the timer starts, when the ball falls through the second beam a know distance further down the timer stops - taking pictures - small metal ball dropped from rest next to meter ruler and its fall is recorded on video

Question 32

what is independent motion

Answer 32

when one ball is dropped vertically and another horizontally both fall and the same rate - both at the same height at the same time the vertical and horizontal motions of the ball are independent of each other

Question 33

why is the vertical and horizontal motion independent of each other

Answer 33

assuming no air resistance vertical velocity changes due to acceleration of free fall vertical distance and time of flight can be calculated using equation of motion (suvat) horizontal velocity remains constant

Question 34

why does horizontal velocity of projectile remain constant

Answer 34

acceleration and velocity are vectors acceleration of free fall is vertically downwards component of this acceleration is the horizontal direction is zero horizontal acceleration = gcos90 = 0 horizontal velocity therefore unaffected by the ball

Question 35

how do you work out the magnitude of a projectile

Answer 35

from the vertical and horizontal components vx and vy use Pythagoras theorem actual velocity v = square root of vx^2+vy^2

Question 36

how do you work out the angle made by the velocity to the horizontal

Answer 36

tan-1(vy/vx)

Question 37

when a projectile is fired at an angle 0 to the horizontal (ground) how do you work out the motion

Answer 37

horizontal component - vcos0 initial vertial component upwards - vsin0