Topic 4 - Momentum, Energy, Work and Power Flashcards Preview

Additional Physics > Topic 4 - Momentum, Energy, Work and Power > Flashcards

Flashcards in Topic 4 - Momentum, Energy, Work and Power Deck (31):

What is stopping distance?

The distance it takes to stop a car, made up from thinking distance + braking distance


What is thinking distance?

The distance the car travels in the time between the driver noticing the hazard + applying the brakes


What factors affect thinking distance?

-Reaction time: affected by tiredness, drugs, alcohol, age
-Fast you're going: faster you go, further thinking distance


What is braking distance?

The distance the car travels during its deceleration whilst the brakes are being applied, time between the brakes applied + car stopping


What factors affect braking distance?

-Speed: faster = further braking distance
-Mass of vehicle: w/ same brakes, heavy = longer to stop
-Quality of brakes
-Grip: friction between tyres + road surface to stop (depends on road surface, weather, tyres)


What experiment could you do to investigate how much frictional force different surfaces provide?

-Add masses 1 by 1 to mass holder to provide a force on block until eventually slides
-Amount of force (amount of mass) needed to slide block depends on amount of friction between block + surface (like tyres on road surfaces)
-Can use different surfaces
-Smaller frictional force between block + surface = smaller force to make block slide


How does a greater mass/greater velocity affect momentum?

More momentum of an object


What is a vector?

-Has size
-Has direction


Is momentum a vector?



What is the equation for momentum?

Momentum = mass x velocity


What is momentum measured in?

kg m/s


What is the relationship between momentum before and momentum when no external forces act?

-Momentum is conserved


What is the equation relating force, chance in momentum and time?

Force = change in momentum / time

F= t


What is force measured in?



Why are protective features put into cars?

-Slow people over a longer time when they crash
-Take a longer time to change momentum, decreasing force


What protective features are out into cars to increase stopping distance and how does this make the car safer?

-Crumple zones: crumple on impact, increase time taken for car to stop
-Seat belt: stretch so increase time taken for wearer to stop reducing force on chest
-Air bags: slow you down more gradually


How can bubble wrap and an egg be used to demonstrate how crumple zones work?

-Dropping egg on hard floor means they shatter
-Drop onto cushions in foam or build crumple zone of cardboard + bubble wrap
-Collisions happen over longer time so force on egg is smaller
-Reduces the force on the egg


What causes work to be done?

When a force moves an object, energy is transferred and work is done.


What is work done measured in?

Joules, J


What is the formula for work done?

Work done = force x distance moved in the direction of the force


What is the formula linking power, work done and time taken?

Power = work done / time taken


What units can be used to measure power?

Watts, W or J/s (joules of energy per second, 1 W = 1 joule of energy per second)


What is the equation for kinetic energy?

Kinetic energy = 0.5 x mass x velocity^2


Initial kinetic energy = work done by brakes to stop vehicle. What is this in symbols and what happens to work done if you double your speed?

- 0.5 x m x v^2 (velocity) = F (maximum braking force) x d (braking distance)
-Double speed = 2xv, and as v^2 KE increases by factor 4
-F is always maximum possible braking force so d must be increased by factor 4 to balance
-So double speed = 4 x braking distance


What is all energy measured in?



What is the equation for gravitational potential energy?

GPE = mass x g (gravitational field strength, 10 N/kg) x height


What is the gravitational field strength on earth?

10 N/kg


What is the principle of conservation of energy?

Energy can never be created nor destroyed, only transferred from one form to another


What is a principle of energy being useful?

Energy is only useful when it's transferred from one form to another.


How does energy transfer in a falling object?

-GPE converted to KE (principle of conservation of energy)
-Some GPE likely dissipated as heat from air resistance
-Kinetic energy gained = Gravitation potential energy lost


How is energy lost when it is transferred?

-Energy lost to heat/sound
-Heat lost to cooler surroundings, dissipates as less concentrated
-Due to Principle of Conservation of Energy, total energy stays the same so energy is still there but can't be used or collected