Mechanics

Question 1

What is the principle of moments?

Answer 1

For a body to be in equilibrium the sum of its anticlockwise moments about a point must equal the sum of its clockwise moments about that point.

Question 2

What is the formula for the moment of a force?

Answer 2

Moment=f x perpendicular distance from line of action of force.

Question 3

What is a couple?What is the formula for their resultant moment.

Answer 3

They are two equal forces parallel to one another acting in opposite directions on the same body.The formula for their resultant moment is force x distance between them.

Question 4

What is a moment?

Answer 4

It is the turning effect of a force around a turning point.

Question 5

What is the centre of mass?Where is this point for uniform solids?

Answer 5

It is a point on an object where all the weight of the object is perceived to act through.For uniform solids this will be at the centre.

Question 6

When does toppling occur?

Answer 6

It occurs when the line of action of an objects weight falls outside its base.This is because a net clockwise moment is created.

Question 7

What type of design is least stable?

Answer 7

One with a narrow base and high centre of mass.

Question 8

Why can different forces act on a support?

Answer 8

If an object is supported by chair legs for example the closer the centre of mass is to one support the greater the support force is.This is required in order to balance the moments.The moment=fxd lower d requires higher f to balance.

Question 9

What is the instantaneous velocity?

Answer 9

It is the velocity of an object at a given period of time.It is found by drawing a tangent to a point on a curved displacement time graph.

Question 10

What is the average velocity?

Answer 10

It is the total displacement/total time taken

Question 11

What is newtons first law?

Answer 11

An object will remain stationary or move at a constant velocity unless a resultant force is applied to it.

Question 12

What is newtons 2nd law?

Answer 12

F=ma.The acceleration of an object is directly proportional to the resultant force applied to it.

Question 13

What is newtons 3rd law?

Answer 13

If object A exerts a force on object B, object B will exert an equal and opposite force on object A.

Question 14

What is freefall?

Answer 14

This is when an object is falling only under the influence of gravity.The acceleration of the object will be equal to g.

Question 15

Describe how to measure g?

Answer 15

Connect a battery timer electromagnet and switch together.Place a small heavy ball on the electromagnet.Flip the switch and the timer will start.Once the ball hits the trapdoor the circuit will be broken and the timer will stop.Measure the height and record the time taken.Repeat for various heights.Plot a graph of s against t^2.The gradient will equal 1/2g.

Question 16

Describe systematic and random errors in the determine g practical.

Answer 16

Random-If a human records the time their will be human error.
Measurement of height
Systematic
If the timer is not calibrated correctly

Question 17

What is a projectile and what are its main characteristics?

Answer 17

A projectile is an object that falls under the influence of gravity.Its horizontal and vertical components of velocity are independant of each other.Horizontal component is constant as it experiences no acceleration.Vertical component changes as it falls under the influence of g.

Question 18

What effect does air resistance have on a projectile?

Answer 18

It causes a drag force that reduces horizontal distance and horizontal velocity.It reduces the max height reached by the projectile.It makes the descent steeper.

Question 19

What are the characteristics of fluid friction?

Answer 19

It depends on the viscosity of the fluid.
It increases with speed
Depends on shape of object.

Question 20

What are 3 important things to remember about friction?

Answer 20

It always opposes motion
It can never speed things up
It converts KE into heat.

Question 21

How is a lift force generated?

Answer 21

Lift is an upwards force on an object moving through a fluid.The object’s shape causes the direction in which the fluid is moving over it to change.This force exerted by the object acts downwards and perpendicular to the flow of the fluid.Therefore,an equal and opposite force is exerted by the fluid causing the object to rise.

Question 22

What is terminal speed?

Answer 22

This is the speed of an object at which its driving force is equal to the resistive force acting on it.

Question 23

What affects the max speed of a car?

Answer 23

Increase the driving force(better engine)

Reduce the resistive force(streamlined).

Question 24

How does a car reach its terminal speed?

Answer 24

Initially as it accelerates its driving force is much bigger as its speed increases air resistance will increase until it is equal and then will reach terminal velocity.

Question 25

What is the principle of conservation of momentum?

Answer 25

For a system of interacting objects the total momentum of the system is conserved unless acted upon by an external force.

Question 26

What are car safety features designed with in mind?

Answer 26

Their aim is to increase the impact time to reduce the force on the passengers

Question 27

Describe 3 safety features implemented in cars.

Answer 27

Crumple zones-they deform plastically in a collision which increases the impact time and reduces the force on passenegers.
Seat belts-They stretch slightly increasing the time taken for the wearer to stop
Airbags-Increase the time taken for the momentum of the head to reach zero

Question 28

What is the formula for efficiency?

Answer 28

Useful power output/total power input.

Question 29

What is the conservation of energy?

Answer 29

In a closed system energy can neither be created or destroyed it can only be transferred from one form to another.