mechanics physics

Question 1

Give examples of scalar quantities

Answer 1

Distance, speed, mass, temperature

Question 2

Give examples of vector quantities:

Answer 2

Displacement, velocity, force, acceleration

Question 3

What are the two methods in adding two vectors to find magnitude and direction?

Answer 3

Pythagoras and trigonometry

Scale drawings with resultant vectors

Question 4

Formula for resolving horizontal component and for vertical component with a vector

Answer 4

x = Vcos()
y = Vsin()

V is vector
x is horizontal component
y is vertical component

Question 5

`How can you prove a force is in equilibrium

Answer 5

Able to draw a closed triangle
or
Adding horizontal and vertical components so that they equal zero.

Question 6

Define what is means for an object to be at equalibrium

Answer 6

This is when the sum of all forces acting on it must be zero, therefore must have no resultant force.

Question 7

Equation of moment

Answer 7

Moment = Force * perpendicular distance

Question 8

Define a couple:

Answer 8

A couple is a pair of coplanar forces where the two forces are equal in magnitude but opposite in direction

Question 9

What is the principle of moments

Answer 9

That for an object in equilibrium, the sum of the anticlockwise moments abut a pivot is equal to the clockwise moment

Question 10

What is the difference between instantaneous velocity and average velocity?

Answer 10

Instantaneous velocity is the velocity of an object at a specific point in time.
Average velocity is the velocity of an object over a specified time frame.

Question 11

What does the area under an acceleration-time graph represent

Answer 11

The change in velocity

Question 12

In projectile motion what is independent?

Answer 12

The horizontal and vertical components.

Question 13

What is the upward force that acts on liquids

Answer 13

Lift

Question 14

When is terminal speed met?

Answer 14

When all driving forces are equal there is no resultant force.
There is no acceleration so the object moves at constant speed.

Question 15

State all of newton’s laws:

Answer 15

1 - at constant velocity all objects are at rest or travelling until a resultant force is experienced.
2 - F = ma (force of an object is proportional to its acceleration)
3 - for each force experienced by an object, the object exerts an equal and opposite force.

Question 16

What is momentum? and the rules regarding it.

Answer 16

The product of mass and the velocity of an object.
Momentum is conserved before and after the collision

According to Newton’s 2nd law: F = ma, a = Change in V/change in time
Therefore F = Change in mass*velocity/ change in time
Proving force is the rate of change in momentum

F * change in time = Change in mass*velocity (rearranged equation)
Impulse = change in momentum

Question 17

What does the area of a force-time graph indicate?

Answer 17

Change in momentum

Question 18

What is the unit for impulse

Answer 18

As F * change in time (impulse) = Change in mass * velocity
- the unit is kgms^-1

Question 19

What are car’s safety design features and how does this help?

Answer 19

Crumple zones, seat belts and air bags increase impact time.
This causes force exerted on passengers to decrease

Question 20

State the two types of collisions

Answer 20

Elastic - momentum and kinetic energy is conserved
Inelastic - where momentum is conserved and kinetic energy may be transferred to heat, sound

Question 21

Give an example of inelastic collisions:

Answer 21

Explosions as kinetic energy after the collision is greater.
If objects stick together after the collision it is an inelastic collision,

Question 22

Define work done:

Answer 22

The force causing a motion multiplied by the distance travelled in the direction of the force

W = FsCos()

Question 23

Define power

Answer 23

Rate of doing work = the rate of energy transfer

P = W/t
P = Fs/t
Therefore P = Fv

Question 24

What does the area under a force displacement graph indicate?

Answer 24

Area = work done

Question 25

How can two objects balancing on each other be stationary

Answer 25

• When the centre of mass is on the pivot
• The anti and clockwise moments are at equilibrium at the pivot

Question 26

What is the formula of work done

Answer 26

W = F*D

Question 27

If there is a reduction in the time of contact what happens to force

Answer 27

Ft = change in (mv) Therefore force would be larger

Question 28

how can you determine the distance travelled using a velocity-time graph

Answer 28

Find the area

Question 29

When two acrobats swing around a pole, what forces are acting on the pole when one acrobats has a greater mass

Answer 29

• vertical force on the pole increases
• centripetal force would not be equal between acrobats
• because of one with a greater mass have a greater force at the same speed

Question 30

How do you find the impulse

Answer 30

Produce of mass and change in velocity of the mass

Question 31

What happens when perfect elastic collision occurs between two trucks on unequal mass

Answer 31

Perfect elasticity means total momentum and total kinetic energy is conserved
- trucks collide and move in separate directions
- the truck with a lower mass has a higher velocity

Question 32

When looking at the thrust of a rocket what must you consider

Answer 32

The force required to keep the object stationary ( F = mg)
And the force required for it to accelerate ( F = ma )
As a result F = mg + ma

Question 33

Define moment of a force around a point

Answer 33

Product of force and perpendicular distance between a line of action and

Question 34

How would you assume a projectile motion graph would differ if air resistance only affected the horizontal direction?

Answer 34

The maximum height would be the same but reached earlier

The range would be less

Question 35

Explain why vertical velocity would have negligible air resistance and how’d this affect vertical motion

Answer 35

Air resistance is proportion to the speed, if vertical speed is low then air resistance would be negligible

• motion is unchanged vertically due to lack of air resistance