Mechanics

Question 1

What is the equation of work done?

Answer 1

Work done = force x s x cos angle between force and displacement
-force x distance in which the force is applied

Question 2

What is the equation for elastic potential energy?

Answer 2

Force x displacement (or extension)

Question 3

What is energy?

Answer 3

Always conserved!

-Ek = Ep = Eg

Question 4

What is an equation for power?

Answer 4

1. Power = energy / time
2. Power = force x velocity
3. Power = work done / time

Question 5

What is Newton’s third law?

Answer 5

When body A exerts a force, F on body B, body B exerts an equal and opposite force, F on body A
-Every force has a paired equal and opposite force

Question 6

What is Newton’s second law of motion?

Answer 6

When an unbalanced (or resultant) force acts on a body, it will accelerate in the direction of that force. The size of the acceleration may be determined by using the equation F = ma

Question 7

What is Newton’s first law?

Answer 7

A body will remain at rest or continue to move in a straight line with a constant velocity unless it is acted on by an unbalanced force

Question 8

What is the centre of mass?

Answer 8

The point in a body around which the resultant torque due to the pull of gravity is zero

Question 9

What is the principle of moments?

Answer 9

Objects in equilibrium when sun or anti-clockwise moments is equal to sum of clockwise moments

Question 10

How do you work out a moment?

Answer 10

Turning moment = force applied x perpendicular distance from pivot

Question 11

What is a couple?

Answer 11

• A pair of equal and opposite coplanar forces
• A pair of forces that provide a turning effect but no translational movement
• Act in opposite fires thin and are parallel but do not not act along the same line

Question 12

How is a moment of a couple defined?

Answer 12

Force x perpendicular distance between the lines of action of the forces

Question 13

Difference between scalar and vector?

Answer 13

• Scalar only magnitude

- Vector magnitude and direction

Question 14

What is momentum what are the units?

Answer 14

momentum = mass x velocity (kgms-1), kg, ms-1

Question 15

How is momentum conserved?

Answer 15

total momentum before collision = total momentum after collision

Question 16

What are the two types of collision?

Answer 16

• Elastic: where momentum and kinetic energy is conserved i.e.i no energy is dissociated as heat, sound etc
• Inelastic: some of kinetic energy is converted into other forms during collision but momentum is always conserved

Question 17

What is force?

Answer 17

• Rate of change in momentum

- F=delta(mv) / deltat

Question 18

What is impulse?

Answer 18

• impulse = change in momentum
• Ft = mv-mu
• The area under a force time graph

Question 19

How can you reduce impact?

Answer 19

1. Crumple zone: the parts at the front of the car crumple up on impact, this causes the car to take longer to stop, increasing the impact time and so decreasing the force on the passengers
2. Seat belts: these stretch slightly, increasing the time taken for the wearer to stop. this reduced the forces acting on the chest
3. Air bags: these also slow down passenger more gradually and prevent them from hitting hard surfaces inside the car

Question 20

What is the centre of mass?

Answer 20

• point at which all the objects weight acts

- all the mass of the object appears to be concentrated at the centre of mass