Space Time And Motion

Question 1

When can we use suvat equation?s?

Answer 1

Motion with constant acceleration

Question 2

What is free fall

Answer 2

Object undergoing acceleration due to gravity

Question 3

What forces act on an object in free fall?

Answer 3

Only weight force due to gravity

Question 4

How does the rate of free fall differ for different objects?

Answer 4

It doesn’t- all objects free fall at the same rate

Question 5

Outline method to calculate g with a ball bearing and electromagnet

Answer 5

• set up: electromagnet,ball bearing , timer,switch, trapdoor ,computer
• measure height from bottom of ball to trapdoor
• flick switch to simultaneously start timer and disconnect magnet
• circuit breaks when ball hits trapdoor and stops timer
• repeat three timers and take average t
• record for diff heights

Question 6

Outline how to evaluate data for calculating g from ball bearing and electromagnet

Answer 6

• plot graph height against time squared
• as initial v is zero graph is a= 1/2at^2 from suvat equations
• gradient is 1/2g

Question 7

How to decrease uncertainties in calculating g from ball bearing and electromagnet

Answer 7

• small and heavy ball bearing so assume small enough air resistance to ignore it
• small increment ruler
• pick certain ball point to measure from to reduces random height error
• use computer instead of stopwatch so time uncertainty smaller
• could use light gates to automatically calculate v then use v^2=2as
• this method does not include calculating v so could reduce systematic error

Question 8

Outline video camera method for finding g

Answer 8

• video camera metre ruler
• analyse frame by frame making note of distance travellers every 0.1 secs
• create a iterative table calculating velocity and acceleration or do gradient of velocity against time

Question 9

Outline strobe ball method to find g

Answer 9

• Regular camera in a dark room and a strobe light
• set camera to long exposure and drop strobe
• will light up at regular intervals and appear multiple times
• calculate change in distance between each location use to find g

Question 10

How to reduce uncertainties in video techniques to find g

Answer 10

• measuring distance is main uncertainty
• parallax error
• time uncertainty reduced with smaller time intervals by increasing frequency or higher frame rate
• repeats
• large distance and small time increments

Question 11

How can u find initial velocity from a velocity time graph for constant acceleration?

Answer 11

Y intercept

Question 12

Definition for Newton’s first law

Answer 12

Body will remain at rest of moving at constant speed in a straight line unless acted on by a resultant force

Question 13

What is Newton’s second law

Answer 13

F=ma force of an object is proportional to acceleration

Question 14

Definition of newtons 3rd law

Answer 14

When an object a exerts a force on object b , object b exerts and equal and opposite force (of the same type) on object a

Question 15

What is newtons 3rd law a consequence of ?

Answer 15

Conservation of momentum as resultant force means change in mass or acceleration and therefore change in momentum which must be conserved so must be equal and opposite force to conserve

Question 16

What can be said about momentum?

Answer 16

Always conserved

Momentum before collision= momentum after

Question 17

What does elastic collision mean?

Answer 17

Kinetic energy and momentum conserved, No energy dissipated

Question 18

What is an inelastic collision?

Answer 18

Kinetic energy not conserved, dissipated to heat sound etc

Question 19

How does Newton’s second law link to momentum ?

Answer 19

Force is rate of change of momentum

F=mv/t

Question 20

When does F=ma not apply? What equation does apply.

Answer 20

When accelerating close to the speed of light mass is changing and equation no longer applys,
F=mv/t does

Question 21

What is impulse? What is it equal to

Answer 21

Impulse=Fxt= change in momentum

Question 22

What is a drag force?

Answer 22

Frictional force in liquids and gases

Question 23

What is drag force proportional to?

Answer 23

Speed

Question 24

How does shape of object affect friction/drag forces?

Answer 24

Larger surface area,less streamlined, more collisions ,greater resistive forces

Question 25

How do frictional forces affect kinetic energy ?

.

Answer 25

Convert to heat

Question 26

When does an object reach terminal velocity (in terms of forces)

Answer 26

Frictional force= driving force (no resultant force)

Question 27

How does an object reach terminal velocity

Answer 27

Object accelerates from rest, as velocity increases resistive forces increase (proportionally)
Eventually ma=to resistive forces and no resultant force so at terminal velocity

Question 28

Discuss a sky diver reaching terminal velocity?

Answer 28

• accelerates until air resistance=weight (terminal velocity)
• open parachute dramatic increase in surface area so increase in air resistance
• resultant force upwards do decelerates , slows down so air resistance decreases
• reaches new lower velocity terminal velocity which is lower enough to survive landing

Question 29

Outline method to measure terminal velocity of a ball bearing?

Answer 29

• tube with elastic bands at fixed distances filled with viscous (thick,resistant to flow) liquid
• drop ball record time to reach each band w stop watch
• calculate average time gap between bands then average velocity
• when velocity is constant it’s reached terminal velocity

Question 30

What variables can we investigate when measuring terminal velocity?

Answer 30

• liquid: greater viscosity ,greater drag force, lower term velocity
• change shape: greater surface area, less stream lined, greater drag , lower term velocity
• increase mass: greater weight force, greater drag force required to balance, greater terminal velocity

Question 31

What is work done a measure of?

Answer 31

Amount of Energy transferred

Question 32

What is the definition of the joule

Answer 32

Work done equation tells us:

Work done when force of one newton moves an object one metre

Question 33

What is definition of power?

Answer 33

Rate of energy transferred

Question 34

Energy cannot be..

Answer 34

Created or destroyed only transferred

Question 35

What is the equation for efficiency in terms of energy?

Answer 35

Efficiency= (useful energy output/ total energy input ) x 100%

Question 36

When we ignore friction ( no energy dissipation) then sum of kinetic and potential energy is …..

Answer 36

Always constant