P10 Forces and Motion Flashcards
What is the equation for the resultant force?
Fres=massxacceleration
What does newton’s second law say?
acceleration is proportional to the resultant force and inversely proportional to the mass
What is inertia?
The tendency of an object to stay at rest or at uniform velocity if no other forces are acting upon it.
What is inertial mass and its formula?
The difficulty of changing an objects velocity
force/acceleration
If the velocity of an object changes, what must be happening?
The resultant force is acting upon it in the same direction as the acceleration
The difference between mass and weight.
Weight is your mass x gravitational field strength and is the force acting upon a object measured in Newtons
Mass is the quantity of matter in an object measured in Kilograms
What is terminal velocity?
As an object falls through a fluid its acceleration decreases as it drag force increase the more the speed.Then the weight is balanced with the frictional forces and the resultant force is zero,then the velocity will be constant and it will fall at that speed.
What’s newtons first law of motion?
According to Newton’s first law of motion, an object remains in the same state of motion unless a
resultant force
acts on it. If the resultant force on an object is zero also known inertia
What is newton’s third law?
According to Newton’s third law of motion, whenever two objects interact, they exert equal and opposite forces on each other.
This is often worded as ‘every action has an equal and opposite reaction’.
What direction does friction act on a moving object?
Opposite to the movement.
What is the formula of stopping distance?
Stopping distance=thinking distance+braking distance
What are factors affecting thinking distance?
Tiredness, drugs, alcohol, distractions and how fast the the car is going a the higher the velocity, the higher the thinking distance needed to stop the car.
What are factors affecting breaking distance?
The road conditions, the car tyres and brakes as they might be worn out, the speed and mass of the car
What is the formula for momentum
p=mv
momentum(kg/m/s)=mass(kg)*velocity(m/s)
Momentum is a _____ quantity?
vector
Momentum is also ________ what?
conserved as it is a closed system
What happens in an elastic collision
the two objects bounce of each other
What happens in a inelastic collision?
The objects stick to each other and move in the greater momentum direction.
What happens in an explosion
The two objects move away from each other
change in momentum formula?
Δp=mΔv
What is the law of the conservation of momentum
total momentum before= total momentum after
In an explosion what are the two objects momentum add up to
obj 1 momentum +obj 2 momentum =0
(The total momentum before is zero so by the law of conservation of momentum the momentum after is also zero.)
What is the formula for impulse?
Impulse = forceTime
(newton seconds)
What is impulse?
change in momentum
In a collision, momentum is not always conserved WHy?
an external force acts (on the colliding objects)
When a speed of a car is doubled why is the thinking distance doubled and why is the breaking distance more than doubled?
thinking distance proportional to speed
as reaction time is constant
when speed doubled and braking force constant, braking time greater
so braking distance more than doubles (think about area under
velocity–time graph)
Example: Calculate the momentum of an 80kg rugby player running at 5m/s
80 kg × 5 m/s = 400 kg m/s
A 60kg and an 80kg skater push away from each other.The 60kg skater moves away at 2.0m/s. a) Calculate her momentum and the other skater’s velocity
a)120 kg m/s
b)80v = 60 × 2.0 kg m/s
v = 60 × 2.0/80
= 1.5 m/s
A 600kg cannon recoils at a speed of 0.5m/s when a 12 kg cannon balls leaves it.
Calculate the velocity of the cannon ball when it leaves the cannon.
12v = 600 × 0.5 kg m/s
∴ v = 600 × 0.5/12
= 25 m/s
When a passenger wears a seat belt explain why it reduces the impact force?
seat belt increases time taken to stop person
so change of momentum per second less ∴ force on person less
An 800kg car travelling at 30m/s breaks.Calculate the amount of breaking force required to stop the car in 6 seconds
Force = change of momentum/time taken =
800 kg × 30 m/s
6.0 s
= 4000 N
What is meant by the limit of proportionality?
limit beyond which tension no longer proportional to extension
What is the spring constant?
force per unit extension as long as limit of proportionality not reached
What is hookes law?
extension of spring directly proportional to force applied as long as limit
of proportionality not exceeded
What is the extension
increase in length from its original unstretched length
