P2.2 The kinetic energy of objects speeding up or slowing down Flashcards
In the equation to find work done,
W=F x d
what do each of the letters stand for and what are the units?
W- work done (J)
F-force applied (N)
d- distance moved in the direction of the force (m)
What is transferred when work is done?
energy
Why do most meteors burn up?
when meteors enter the atmosphere they have high kinetic energy. Friction transfers some of the kinetic energy into heat energy and work is done. The temperature becomes so extreme that most meteors burn up.
What is power?
the work done or energy transferred in a give time
In the equation
P= E (divided by) T
what do the letters stand for and what are the units?
P- power (W)
E- energy transferred (J)
t- time taken (s)
What is gravitational potential energy?
the energy that an object has because of its position in a gravitational field
On earth, what is the gravitational field strength approximately?
10 N/kg
What happens when an object is raised vertically?
Work is done against the force of gravity and the object gains gravitational potential energy
In the equation
Ep = m x g x h
what do each of the letters stand for and what are the units?
Ep- change in gravitational potential energy (J)
m- mass (kg)
g- gravitational field strength (N/kg)
h- change in height (m)
What does kinetic energy depend on?
The mass and speed of an object
In the equation
Ek= 0.5 x m x v2
what do each of the letters stand for and what are the units?
Ek- kinetic energy (J)
m- mass (kg)
v- speed (m/s)
In a car, what happens to the kinetic energy when the car slows down?
Energy is converted into other types of energy (conservation of mass)
kinetic energy is converted to heat energy as friction between the wheels and brake pads, causing the temperature of the breaks to increase
A falling object converts gravitational potential energy into…
kinetic energy
so
Kinetic energy gained = Potential energy lost
What is a powerful machine?
a machine which transfers a lot of energy in a short space of time
What is one watt?
1 joule of energy transferred per second
so 1 watt = 1 J/s
What happens when a force causes an object to move through a distance?
work in done
What is momentum?
a property of moving objects
The greater the …………and………… of an object, the greater its momentum
mass
velocity
in the equation
p= m x v
What do the letters stand for and what are the units?
p- momentum (kg m/s)
m- mass (kg)
v- velocity- (m/s)
What is the conservation of momentum?
in a closed system, the total momentum before an event is equal to the total momentum after the event. This is called conservation of momentum
Describe a regenerative braking system in cars
Rather than converting the kinetic energy of the vehicle into heat energy to slow it down, the brakes put the vehicles motor into reverse
with the motor running backwards, the wheels are slowed
The motor also acts as an electrical generator, converting kinetic energy into electrical energy that is stored as chemical energy in the car’s battery
- they STORE energy instead of wasting it
Why are car crashes dangerous for people inside the car?
causes car to slow down really quickly- means lots of kinetic energy is converted into other form of energy in a short period of time
Also will be a big change of momentum over a very short time so people inside car feel huge forces
In general, how are cars designed to be safer incase there is a crash?
designed to convert kinetic energy of the car and its passengers in the way that’s safest for the car occupants.
They do this by INCREASING THE TIME OVER WHICH MOMENTUM CHANGES HAPPEN, WHICH LESSENS THE FORCES ON THE PASSENGERS
Evaluate the use of crumple zones in cars
- at the front and back of car. crumple upon impact
- car’s kinetic energy is converted into other forms of energy by the car body as it changes shape
- crumple zones INCREASE THE IMPACT TIME, decreasing the force produced by the change of momentum
Evaluate the use of side impact bars in cars
- are strong metal tubes fitted into car door panels
- help direct the kinetic energy of the crash away from the passengers to other areas of the car such as crumple zones
Evaluate the use of seat belts in cars
- stretch slightly, increasing the time taken for the wearer to stop
- reduces the forces acting on the chest
- some of the kinetic energy of the wearer is absorbed by the seatbelt stretching
Evaluate the use of air bags in cars
- slow you down more gradually
- prevent you from hitting hard surfaces inside the car
What is the unit of weight?
newton
The total momentum of 2 cars was not conserved
what does this mean?
The momentum before does not equal the momentum after
Why would a seatbelt that produces a constant force after collision be better for a car driver?
As it reduces the momentum of the driver
a smaller force would be needed
Why is the speed of someone at the bottom of a slide less than the calculated maximum speed?
As work is done
against friction between the miner and the slide
due to the slide not being perfectly smooth
this causes kinetic energy to be transferred as heat energy to the surroundings
What are some benefits of a car being fitted with a regenerative breaking system?
the battery needs recharging less often
lower fuel costs
efficiency of the car is increased as work done charges the batteries
