Unit 4 Mechanics

Question 1

Define scalar and vector quantities.

Answer 1

Scalar quantities have magnitude only and vector quantities have magnitude and direction

Question 2

What is an object at equilibrium?

Answer 2

Object at rest or moving with a constant velocity

Question 3

State the conditions for an object to be in equilibrium

Answer 3

The resultant force on it must be zero.
The total clockwise moment about any point on the object must equal the total anticlockwise moment about that point

Question 4

Define the moment of a force about a point

Answer 4

Moment = force x perpendicular distance from the point to the line of action of the force

Question 5

Define the moment of a couple

Answer 5

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

Question 6

What does the principle of moments state?

Answer 6

Sum of clockwise moments about any point = sum of anticlockwise moments about that point

Question 7

Define centre of mass.

Answer 7

The point through which a single force has no turning effect when applied - it is the point at which the weight of a body acts. An object will topple over if the line of action of its weight is outside of its base.

Question 8

How is steady speed represented on a displacement time graph?

Answer 8

Straight line with a constant gradient

Question 9

What does a curved line on a velocity time graph represent?

Answer 9

Changing acceleration

Question 10

What does a value of zero on an object’s acceleration - time graph indicate?

Answer 10

Object is moving with constant velocity

Question 11

What are the conditions for an object to be in free fall?

Answer 11

Only has its weight (force of gravity) acting on it

Question 12

Give the properties for the motion of a projectile

Answer 12

Acceleration is due to gravity, is always acting downwards, and only affects the vertical motion of the object
Horizontal velocity is always constant because there is no horizontal force or acceleration

Question 13

What happens to the trajectory of a projectile if air resistance acts on it?

Answer 13

Downward trajectory will be steeper than upward trajectory
Its horizontal speed, range and maximum height will be reduced

Question 14

State properties of drag (frictional forces)

Answer 14

Acts in the opposite direction to an object’s movement
Increases with increasing viscosity of a fluid
Increases with increasing speed of an object
Dependant on the shape and size of the object
Causes a moving object to slow down and stop if there is no force propelling it

Question 15

Define inertia

Answer 15

Inertia is the tendency of objects in motion to stay in motion, and objects at rest to stay at rest

Question 16

State Newton’s first law of motion

Answer 16

Velocity of an object will only change is a resultant force is acting on it

Question 17

State Newton’s second law of motion

Answer 17

Acceleration of an object is proportional to the resultant force on the object and inversely proportional to the mass of the object

Question 18

What are the properties of a pair of forces related by Newton’s third law?

Answer 18

Same size
Act on separate objects
Act in opposite directions
Along the same line
Same type

Question 19

What happens in an elastic collision?

Answer 19

Kinetic energy is conserved - the objects involved will have the same kinetic energy after the collision as before

Question 20

What happens in an inelastic collision?

Answer 20

Kinetic energy is not conserved - the objects involved will have less kinetic energy after the collision than before

Question 21

What is the principle of conservation of momentum?

Answer 21

Total momentum before two objects collide = total momentum after they collide

Question 22

State Newton’s second law in terms of momentum

Answer 22

Force acting on an object is equal to rate of change of momentum of the object

Question 23

State the relationship between impulse and momentum

Answer 23

Impulse = change of momentum

Question 24

What does the area under the line of a force time graph represent?

Answer 24

Impulse of the force or object change in momentum

Question 25

How do many everyday safety features reduce the force of an impact?

Answer 25

Increase time taken for, a change in momentum, reducing impact force

Question 26

Define power

Answer 26

Rate of energy transfer or rate of doing work
Power = force x velocity

Question 27

Define efficiency

Answer 27

Measure of how much energy is wasted in an energy transfer

Question 28

State the principle of conservation of energy

Answer 28

Energy cannot be created or destroyed, only transferred between different stores and objects