# P5b: Vectors and Equations of Motion

When analysing the motion of objects, knowing how fast they are travelling is only half the information. We also need to know the direction that they are travelling in. Two cars travelling towards each other at high speed is entirely different from the same cars travelling at the same speed in the same direction.

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What is important when describing the motion of an object?
Direction
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What does relative speed depend on?
The direction of movement
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Talk about relative speed (RS) and the direction of movement for two cars travelling at 15 m/s.
If they are side by side&travelling in the same direction,their RS is 0.Someone looking across from one car to the other will see the other car keeping pace with them.If the two cars r travelling in opposite directions,their RS will be 30 m/s(15+15)
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What is not important when measuring speed?
Direction.
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What quantity is speed?
A scalar quantity
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Equation to work out distance: - using average speed and time
average speed x time
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How do you work out average speed?
Initial speed + Final speed / 2 (u+v/2)
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How do you calculate final speed?
initial speed + (accelerate x time) (u + at)
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What is a scalar quantity?
A scalar quantity is a quantity in which direction is not important. All that matters is its magnitude (its size)
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What is a vector quantity?
A vector quantity is a quantity in which direction is important
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Give two examples of scalar quantities
time, mass
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Give three examples of vector quantities
acceleration, force, velocity
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How do you calculate if two vectors are parallel?
Add the vectors together - taking in their direction
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What is a resultant vector?
a single vector that would replace two other vectors.
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Work out the resultant vector: Two forces, 5 N and 8 N, act in the same direction.
The resultant force is 5 + 8 = 13 N.
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Work out the resultant vector: Two objects travel in opposite directions, one at 5 m/s and the other at 8 m/s.
The resultant velocity is 3 m/s in the direction of the 8 m/s object.
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How do you calculate final speed squared?
u^2 + 2as (initial speed squared + (2 x acceleration x distance)
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How do you calculate distance? - using time, initial speed and acceleration
ut + 1/2 at^2 ((initial speed x time) + (0.5 x acceleration x time squared))
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Why is speed a scalar quantity?
it is the rate of change in the distance travelled by an object
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Why is velocity a vector quantity?
it is the speed of an object in a particular direction.
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## Other cards in this set

### Card 2

#### Front

What does relative speed depend on?

#### Back

The direction of movement

### Card 3

#### Front

Talk about relative speed (RS) and the direction of movement for two cars travelling at 15 m/s.

### Card 4

#### Front

What is not important when measuring speed?

### Card 5

#### Front

What quantity is speed?