Mechanics

Question 1

What is Newton’s first law?

Answer 1

An object will remain at rest or constant velocity unless a resultant force is acting on it.

Question 2

What is a moment?

Answer 2

The turning force of an object about a pivot.
Or
A turning moment is the force x perpendicular distance of the force from the pivot.

Question 3

How is a moment calculated?

Answer 3

Moment = Force x Distance (perpendicular)

Question 4

What is the relationship between clock and anti-clock moments when an object is at equilibrium?

Answer 4

sum of anti-clock moments = sum of clock moments

Question 5

Where does weight act through on an object?

Answer 5

Its centre of mass.

Question 6

For an object on pivot to be in eqilibrium, what relationship should all forces acting on it have?

Answer 6

Sum of all moments (clock and anti-clock) around pivot must equal 0.
Sum of all vertical forces must equal 0.

Question 7

What is a torque?

Answer 7

When a couple, a pair of equal and opposite forces acting on different lines, produce a turning moment it is called a torque.

Question 8

How do you calculate torque?

Answer 8

T = Fd
Torque = Force x distance

Question 9

What is stable equilibrium?

Answer 9

If the object is displaced, it will return to equilibrium when released.

Question 10

What is unstable equilibrium?

Answer 10

If an object is displaced, it will move further away from equilibrium when released.

Question 11

What is Newtons 2nd law?

Answer 11

Force is equal to the rate of change of momentum. F = ma

Question 12

What is Newton’s 3rd law?

Answer 12

For every action there is an equal and opposite reaction.

Question 13

What is kinetic energy?

Answer 13

The energy due to the motion of an object.

Question 14

What is potential energy?

Answer 14

The energy due to position. As an object rises it gains potential energy.

Question 15

When does ½mv² no longer hold for finding kinetic energy?

Answer 15

At relativistic speeds (close to the speed of light)

Question 16

When does mgΔh not hold for finding potential energy?

Answer 16

When the gravitational field is not uniform

Question 17

What is the equation for power (mechanics)?

Answer 17

P = w/t 
P = Fd/t
P = Fv

Question 18

What is the equation for efficiency?

Answer 18

Useful power output / total power input

Question 19

How does a rocket engine work?

Answer 19

The rocket engine is decreasing in mass but the momentum is staying the same so the velocity must increase.

Question 20

What is an elastic collision?

Answer 20

A collision where kinetic energy is conserved

Question 21

What is an inelastic collision?

Answer 21

A collision where kinetic after collision is less than before the collision.

Question 22

What are the 8 energy stores?

Answer 22

Thermal
Electrostatic
Chemical
Kinetic
Magnetic
Elastic potential 
Nuclear
Gravitational potential

Question 23

What are the types of energy transfer?

Answer 23

Mechanical (work done)
Radiation (waves)
Electrical
Heating

Question 24

What’s the difference between power, work done and energy?

Answer 24

Work done is energy transferred.
Power is rate of energy transferred.
Energy is the capacity of an object to do work.

Question 25

Why do seatbelts work?

Answer 25

F = (mv - mu) / t

So increasing time during the change in p reduces the force exerted on the person.

Question 26

What is the conservation of momentum?

Answer 26

Momentum is always conserved in a closed system.

Momentum before event = momentum after event

Question 27

How can efficiency be improved?

Answer 27

Use oil on moving parts
Fluorescent lamp instead of bulb
Streamline
Insulate

Question 28

What happens in terms of forces when a powered object increases its speed?

Answer 28

It’s output force exceeds the resistive force.

Question 29

How do you find the speed of trolley collision with a block just before impact?

Answer 29

Place a piece of card on the trolley.
Use a light gate just in front of block and find the time it was obscured.
Find v using:
v = length of card / time

Question 30

What is the centre of mass of an object?

Answer 30

The point at which the weight of an object acts through.
The point through which a force produces no turning effect.