Mechanics

Question 1

Give examples of scalar and vector quantities

Answer 1

Scalar: mass, temperature, time, length

Vectors: force, displacement, acceleration, momentum

Question 2

How to calculate average speed?

Answer 2

Total distance / total time

Question 3

What is relative speed?

Answer 3

The comparison of speed between two objects

Question 4

If your car goes left at 30mph and a car goes left at 40mph, what is the speed relative to your car?

Answer 4

10mph left

Question 5

If your car goes right at 30mph and a car goes left at 40mph, what is the speed relative to your car?

Answer 5

70mph left

Question 6

If a plane flies right at 120mph and wind goes left at 10mph, what is the resultant velocity?

Answer 6

110mph right

Question 7

How to work out the velocity if the forces are on a right angle

Answer 7

Draw it on a graph, create a triangle then use pythag to find the hypotenuse (as you connect vectors end to end)

For the direction, do trig

Question 8

What is displacement?

Answer 8

The distance from the start to the finish, in a straight line

Question 9

What is a projectile?

Answer 9

Something that is projected or dropped and only has gravity acting on it (ignoring air resistance)

Question 10

What is a trajectory?

Answer 10

The path a projectile takes through the air

It is always a parabola (a rainbow shape)

Question 11

How do you calculate a projectiles trajectory?

Answer 11

Calculate the horizontal bit (which is a constant velocity as gravity doesn’t act on it)

Then the vertical bit (which will increase as gravity accelerates it)

Then add them together

Question 12

What angle should you push on an object to get maximum moment?

Answer 12

Right angle, as any other angle means a smaller moment because the perpendicular distance between the line of action and pivot is smaller

Question 13

If an object is suspended in air, where would the centre of mass be?

Answer 13

Directly below the suspension

If it swings it will continue swinging until it reaches below the suspension again

Question 14

Why does the centre of mass rest below the suspension of a suspended object?

Answer 14

Because there is no moment, as the pivot is the suspension and is in line with the line of action

Question 15

How do you find the centre of mass for any flat shape via suspension?

Answer 15

Hang it once and see where it stops moving

Then hang it in a different position and wait for it to stop moving

The place where the two lines both go through is the centre of mass

Question 16

How to find the centre of mass for simple 2d shapes

Answer 16

Via lines of symmetry

Question 17

What happens if the anti-clockwise moment equals the clockwise moment?

Answer 17

The object won’t turn as it is balanced

Question 18

What happens if the anti-clockwise moment is not equal to the clockwise moment?

Answer 18

There is a resultant moment and the object turns

Question 19

What makes a stable object? (moment)

Answer 19

A wide base and low centre of mass

Question 20

When will an object tip over due to moments?

Answer 20

If it’s centre of mass moves beyond the edge of its base

Question 21

What is a centripetal force?

Answer 21

The force that keeps something moving In a circle

Question 22

What are the three forces that can cause a centripetal force?

Answer 22

Friction, tension and gravity

Question 23

What is the centripetal force of a car going round a bend?

Answer 23

Friction, as the car is drawn towards the middle of the bend due to the friction of the tires

Question 24

What three things can change the size of a centripetal force?

Answer 24

Mass - the heavier an object is the greater the force to keep it in a circle

Speed - the faster an object is the greater the force needed to keep it

Radius - the smaller the circle, the more turns the object has to do so a greater force is needed

Question 25

What are geosynchronous satellites?

Answer 25

Satellites that are put in high orbit and rotate with the earth, therefore staying in the same place above the earth These are normally communications as they’re always in the same place so tv and phones can find it

Question 26

What are low-polar orbit satellites?

Answer 26

Satellites that are closer to the earth and spin round both poles as the earth rotates the other way beneath them They go much faster as gravity is stronger and can take pictures of the earth as they’re low Used for weather and spying

Question 27

How does ‘orbit’ work?

Answer 27

Orbit is the balance of the forward motion of the object (velocity) and the force (gravity) pulling it into the circle This subsequently makes it go round in circles

Question 28

Why do planets further away from the sun move slower?

Answer 28

Gravity makes things move faster as the pull is stronger so there’s a stronger force of attraction If you move away from the sun the gravity is weaker so you move slower

Question 29

Why does a comet speed up when it orbits close to the sun?

Answer 29

Because as it gets closer, it speeds up due to gravity

Question 30

Do transformers work on DC?

Answer 30

No, only AC as they use electromagnetic induction

Question 31

What are the three types of transformers?

Answer 31

Step up Step down Isolating

Question 32

What do step up transformers look like?

Answer 32

They have more turns on the secondary coil than the primary coil

Question 33

What do step down transformers look like?

Answer 33

They have more turns on the primary coil than the secondary

Question 34

How do transformers work?

Answer 34

The primary coil produced a magnetic field which stays within the iron core This means nearly all of it passes through the secondary coil (hardly any is lost) There is AC in the primary coil the field in the iron core is constantly changing direction This rapidly changing field is then felt by the secondary coil This induced an alternating voltage in the secondary coil The number of turns on the two coils determine whether the voltage is greater or less than the voltage in the primary

Question 35

What if you supplied DC to the primary coil?

Answer 35

You’d get nothing out of the secondary, as although there’s still a field it is not alternating

Question 36

What is the iron core in transformers used for?

Answer 36

Transferring the changing magnetic field No current flows through it

Question 37

Are transformers efficient?

Answer 37

They’re nearly 100% efficient