Topic 2, Mechanics

Question 1

Differentiate betw distance and displacement

Define/explain ‘position’

Answer 1

Displacement is a vector quantity (vector from initial to final position)
Distance is dependent on the path taken (length of path travelled)

point in space // vector from origin to the point in space

Question 2

Differentiate betw speed and velocity

Answer 2

Velocity is a vector quantity
Speed has no direction (only magnitude)

Question 3

What is instantaneous velocity in terms of instantaneous speed (the relationship between these)

Answer 3

Inst. v = Inst speed + the direction
(e.g. 20m/s east)

Question 4

Define acceleration

Answer 4

The rate of change of velocity. (vector quantity)

Question 5

Define velocity

Answer 5

The rate of change of displacement. (vestor quantity)

Question 6

Units acceleration

Answer 6

Speed units / Time units

e.g. (km/h)/s or (m/s)/s = m/s^2

Question 7

Does a negative acceleration mean the object is deaccelerating/slowing down?

Answer 7

No, not necessarily!
If no directions are given, neg implies slowing down.
BUT if directions are given it could simply be accelerating in the “opp” (neg) direction.

Question 8

What happens to an object and its acceleration when the line on a v-t graph crosses the x (the t) axis?

Answer 8

It turns around! If from pos to neg: slows down, truns around (v=0) and speeds up
(on axis y=0 hence v=0 and thus a will = 0

Question 9

Does a v-t graph tell you about the position of an object?

Answer 9

No! Change in positon yes but not actual position

Question 10

How do you know if an object is moving left or right from a v-t graph?

Answer 10

Point above t-axis (pos v) = moving RIGHT

Point below t-axis (v neg) = moving to the LEFT

Question 11

How do you know if an object is slower/faster than another point from a v-t graph?

Answer 11

The closer to the x-axis = the slower it is (lower v), further away=faster. REGARDLESS OF POS/NEG!!
If it goes towards the x axis, it is slowing down

Question 12

How do you know if the acceleration is to the left or right from a v-t graph?

Answer 12

The sign of the slope (pos/neg)!

Neg slope = neg a = LEFT

Pos slope=pos a=RIGHT

Question 13

Tell how fast/slow it is going from v-t graph =

Answer 13

= d from t-axis; closer=slower

Question 14

Find average velocity from x-t graph

Answer 14

delta x / delta t
slope of the secant betw 2 points
(take average betw final and initial point)

Question 15

Find instantaneous velocity from x-t graph

Answer 15

= slope of the tangent line at the point
(draw tangent line, find 2 points (if grid, where lines meet) and find gradient = inst v)

Question 16

What do you use a tangent line for?

Answer 16

To calculate ANY RATE!
e.g. v-t graph — inst a = tangent line

Question 17

How do you draw a tangent line?

Answer 17

Passes through the point
Does not pass through other points (further away) gen.
Goes along the line for a while, same each side

Question 18

Do objects of different masses dropped from the same height reach the ground at the same time (i.e. does a=g)?

Answer 18

Only if NO AIR RESISTANCE (in vaccuum)

Question 19

What is an objects weight dependent on (aside from its mass)?

Answer 19

Its LOCATION (as g differs eg moon, everest, surface earth)

mass is not affected

Question 20

Differentiate betw mass and weight

Answer 20

Weight = m * g
(is dep on location)

Mass only dep matter (not position)

Answer 21

m s^-2 accel due to gravity
N/kg gravitational field strength

Question 22

How do you find the d at point from v-t graph

Question 23

What do you get by taking area under the curve (of a certain time interval) of a v-t graph?

Answer 23

The CHANGE of displacement for that time interval = the FINAL “position”, how much distance moved in that time

Question 24

What is a force?

Answer 24

Pushes/pulls, cause changes in motion

Question 25

What happens to the motion if the force F and velocity v are
1. In the same direction
2. In opposite direction
3. Perpendicular

Answer 25

1. Speeds up
2. Slows down
3. Turns

Question 26

Differentiate between contact and field forces

Answer 26

Direct contact on the object vs no contact (eg gravity)

Question 27

Divide the following forces into contact and field forces.
1. Tension
2. Electrical
3. Gravity
4. Push
5. Normal force
6. Magnetic
7. Frictional

Answer 27

2,3,6 = field, the rest contact

Question 28

How do you draw a FreeBody Diagram? Give the steps

Answer 28

Draw with scale, SHOW LENGTHS; if same size, show that!
(0.5 draw the object, simplified, assume point … F acting from centre of object (centre of mass))
1. Draw the weight (mg) STRAIGHT DOWN (always, no matter if at angle)
2. Search for points of contact (is it on a surface? = normal force, do you have friction? Is there a string attached? = tension force)
3. STOP!! Don’t do anything else!! ONLY FORCES ON FBD, no motion/velocity/acceleration or anything like that

Question 29

What do you use a FBD for?

Answer 29

To find the resultant force, Fres

Question 30

1. Define Newton’s 1st law of motion (law of inertia)
2. Explain what this means in terms of resultant force

Answer 30

1. “An object will remain at rest, or continue to move in a straight line at a constant speed, unless a resultant force acts on it.”
2. If Fnet=0, the velocity is constant (or 0) OR if you know the object moves w constant/zero v (no accélération), thé Fres=0.

Question 31

Define Newton’s 2nd law of motion (+ kinda explain, eq)

Answer 31

“The acceleration of an object is directly proportional to the net (external) force applied, and is indirectly proportional to its mass.”

a=F/m (a prop to F, inversely prop to m, and in the same direction as F)

(Thus also F=ma or F (prop to) ma)

Question 32

Define Newton’s 3rd law of motion

Answer 32

“Whenever one body exerts a force on another body, the second body exerts exactly the same force on the first body, but in the opposite direction.”

Chris Doner also: action/reaction, 1 interaction 2 forces. Forces equal but opposite; acting on 2 diff bodies, force pairs.

Question 33

Define work!! (Key definition!!)

Answer 33

Work is the transfer of energy.

Question 34

Define power (key definition!!)

Answer 34

The rate of transfer//the change in energy. deltaE/deltat