Physics Forces Nov 2018 Flashcards

1
Q

What are the average speeds you need to know?

A
Walking = 1.0 - 2.0 m/s
Jogging = 3.0 - 5.0 m/s
Cycling = 6.0 - 8.0 m/s
Car on local road =  10.0 - 15.0 m/s
Car on motorway = 25.0 - 30.0 m/s
Plane flying = 200.0 m/s
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2
Q

What is the equation for average speed?

A
v = s/t
speed = distanced travelled / time
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3
Q

How do you calculate speed from a distance - time graph?

A

Calculate the gradient of the line

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4
Q

How do you calculate speed from a distance - time graph when there is a curve

A

Draw a tangent at two points of the curve. Calculate the gradients of these tangents and then find an average speed.

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5
Q

What is the formula for acceleration?

A
a = (v - u)/t
acceleration = (final velocity - initial velocity)/time
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6
Q

How can you tell if the object is accelerating or decelerating from numbers?

A

+ number = accelerating

- number = decelerating

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7
Q

How can you calculate the distance travelled from a velocity time graph?

A

Calculate the area underneath the graph

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8
Q

How can you calculate the distance travelled from a velocity time graph if it has an irregular shape? (Very unlikely in an exam)

A

Count all the whole squares under the graph and estimate the incomplete squares. Add together to get a total

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9
Q

What is the equation for acceleration when it is linked with displacement?

A

v2 - u2 = 2as

final velocity squared - initial velocity squared = 2 x acceleration x displacement

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10
Q

What is Newton’s 1st law?

A

An object will stay stationary or at a constant speed unless acted upon by an unbalanced/resultant force

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11
Q

What is Newton’s 2nd law?

A

When an unbalanced force acts upon an object it accelerates. The object can accelerate, decelerate or change direction. A larger force creates a larger acceleration and a larger mass is harder to accelerate

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12
Q

What is Newton’s 3rd law?

A

For every action there is an equal and opposite reaction. In every interaction there is a pair of forces acting on two objects. The size of the force on the first object equals the force on the second. The direction of force on the first object is opposite to the direction of force on the second.

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13
Q

What is the equation for Newton’s 2nd law?

A
f = ma
Force = mass x acceleration
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14
Q

What is the equation for stopping distance?

A

Stopping distance = thinking distance + braking distance

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15
Q

What factors can affect thinking distance?

A

Tiredness, alcohol, drugs, distractions (e.g. phones) & speed travelling at

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16
Q

What factors can affect braking distance?

A

Quality of road, weather conditions, car conditions, mass of car, force exerted on the pedal & speed travelling at

17
Q

What is the equation for braking distance and change in kinetic energy?

A

Fs = 1/2mv2

work done = change in kinetic energy

18
Q

What is the equation for momentum?

A
p = mv
Momentum = mass x velocity
19
Q

What must you do with momentum for two objects coming together?

A

Have a +/- direction

20
Q

What is the equation for force with change of momentum?

A

is f = ma we can substitute a for (v-u)/t. This makes

f = m(v-u)/t. (mv-mu = change in momentum)

21
Q

What is the definition of a scalar?

A

A quantity with only magnitude (size) and no direction

22
Q

What is the definition of a vector?

A

A quantity with magnitude (size) and direction

23
Q

What is velocity?

A

A speed in a defined direction

24
Q

What is displacement?

A

A distance travelled in a defined direction

25
Q

What is a force?

A

A push or a pull

26
Q

What are the two types of forces? Definitions?

A

Contact Force - a force between two objects when they touch

Non-contact Force - a force between two objects that are physically separated

27
Q

What is the unit for forces?

A

N - Newtons

28
Q

What is the equation for weight?

A
W = mg
Weight = mass x gravitational field strength
29
Q

What is the centre of mass?

A

The point through which the weight of an object can be taken to act

30
Q

What is the resultant force?

A

A single force that has the same affect as all the forces together

31
Q

How do you work out the resultant force?

A

Biggest number - smallest number = resultant force in direction of bigger number

32
Q

What is momentum?

A

The product of mass and velocity