Section 4 - Mechanics and Materials: 4.1 - Mechanics

Question 1

What is meant by a scalar quantity?

Answer 1

A quantity that has only magnitude.

Question 2

What is a vector quantity?

Answer 2

A quantity that has magnitude as well as
direction.

Question 3

Is acceleration a vector or scalar quantity?

Answer 3

Vector.

Question 4

Is mass a scalar or vector quantity?

Answer 4

Scalar.

Question 5

What is the difference between mass and weight?

Answer 5

Mass is scalar and is not dependent on the
gravity acting upon it. Weight is a vector and
depends on the gravitational field strength.

W = mg

Question 6

If an object is in equilibrium the sum of the anti
clockwise moments would be …..

Answer 6

Equal to the sum of the clockwise
moments (principle of moments).

Question 7

If an object is in equilibrium it means the object is …

Answer 7

Not accelerating, so is either:

● Stationary, or
● Moving at a constant velocity

Question 8

How can the forces acting on a object be shown to be in equilibrium?

Answer 8

Adding the horizontal and vertical components of the forces acting on it, showing they equal zero.
Or if there are 3 forces acting on the object you can draw a scale diagram, if the scale diagram forms a closed triangle, then the object is is equilibrium.

Question 9

What is a moment?

Answer 9

A turning force: force multiplied by the
perpendicular distance from the point to
the line of action of the force.

Question 10

What is meant by a couple?

Answer 10

A pair of equal and opposite coplanar forces.

Question 11

What is meant by the centre of mass?

Answer 11

The point through which all the mass of an object acts, for a uniform object the centre of mass is the centre of the object

Question 12

If you have a uniform object, where
would its centre of mass be?

Answer 12

At the centre of the solid.

Question 13

What can be described as ‘the change in

displacement per unit of time’?

Answer 13

Velocity, instantaneous velocity can be
found by measuring the gradient of a
tangent to a displacement-time graph

Question 14

What is the area under a velocity-time and
acceleration-time graph?

Answer 14

The displacement travelled and the
velocity respectively.

Question 15

As speed increases, so air resistance ….

Answer 15

Increases (proportional to the square of
the speed).

Question 16

A ball if projected off a castle at 6m/s,
how does its horizontal velocity change
from its launch until it hits the ground?

Answer 16

The horizontal velocity remains the same
as there is no acceleration in that
direction.

Question 17

How do the SUVAT equations reflect that all objects fall at the same rate?

Answer 17

Mass is not included in the SUVAT
equations, showing that the mass of an
object does not affect its speed or
acceleration.

Question 18

In projectile motion, what is the vertical acceleration?

Answer 18

The vertical acceleration is equal to
gravitational field strength (g).

Question 19

What is meant by terminal velocity?

Answer 19

When the forces acting on the falling
object become balanced, the
acceleration becomes zero and the
object is moving at maximum velocity.

Question 20

What is meant by friction?

Answer 20

A resistance to motion between an object
and a surface or an object moving
through a fluid. Friction is a force that
acts in the opposite direction to the
movement.

Question 21

Which of Newton’s Laws state ‘every action force
has an equal and opposite reaction force’?

Answer 21

Newton’s third law?

Question 22

What is Newton’s second law?

Answer 22

Where mass (m) is constant, F is the
force applied and a is the acceleration.

Question 23

What is Newton’s first law?

Answer 23

An object stays moving at a constant
velocity until a force acts upon it.

Question 24

What is the difference between elastic
and inelastic collisions?

Answer 24

In an elastic collision the kinetic energy before is
equal to the kinetic energy afterwards.

In an inelastic collision the kinetic energy at the
end is not equal to the kinetic energy at the start.

Question 25

Give an equation that can be used to calculate
momentum.

Answer 25

momentum = mass × velocity

Question 26

True or false: ‘Linear momentum is only

conserved in elastic collisions.’

Answer 26

False, linear momentum is always conserved.

Question 27

The rate of change of momentum can
also be described as…

Answer 27

Force.

Question 28

What is impulse?

Answer 28

The change in momentum.
F∆t = ∆mv

Question 29

What does the area underneath a force
time graph represent?

Answer 29

Impulse, the change in momentum.

Question 30

Fs cos(θ) = ?

Answer 30

The work done / the energy transferred

Question 31

What’s the rate of work done equal to?

Answer 31

The power.

Question 32

What is efficiency?

Answer 32

Efficiency = The useful output power /
input power

Question 33

What is meant by the principle of conservation of energy?

Answer 33

Energy cannot be created or destroyed, only
transferred into other forms of energy.

Therefore the total every in a closed system
will always remain the same.

Question 34

A river flowing to the right acts on a crossing boat with force 19N, the boat
provides a perpendicular thrust of 45N, what is the resultant force on the boat?

Answer 34

Forces are perpendicular so use pythagoras’s theorem.
Resultant force2=192+452
Resultant force = 48.84669897 N
Resultant force= 49N (2sf)
Direction, tanθ= 45/19 θ= tan-1(45/19)
θ=67° above the horizontal

Question 35

A ball is fired at a velocity of 10 m/s, at an angle of
30° from the horizontal, find the vertical and
horizontal components of velocity.

Answer 35

x = 10 cos 30° y = 10 sin 30°
= 8.7 m/s = 5 m/s

Question 36

What is lift?

Answer 36

An upward force which acts on objects
travelling in a fluid, it is caused by the
object creating a change in direction of
fluid flow and acts perpendicular to the
direction of fluid flow.