P2.3 - Work, Energy & Momentum Flashcards
What is the relationship between work and energy?
Energy transferred = work done
What is “work” in science?
Work is done when a force makes an object move.
How is the work done by a force calculated?
Work done (J) = force (N) x distance in the direction of the force (m)
What happens to the work done to overcome friction?
The work done is transferred as energy that heats the objects and the surroundings.
What does the GPE of an object depend on?
Its weight and how far it moves vertically.
What happens to the GPE of an object moves up or down?
It increases when the object goes up and decreases when the object does down.
How is the change in GPE calculated?
Mass x gravitational field strength x Δheight
Give the equation for change in GPE.
Ep = mgh
What does the KE of an object depend on?
Mass and speed.
How is KE calculated?
KE (J) = 0.5 x mass (kg) x speed^2 (ms^-1)^2
What is elastic potential energy?
The energy stored in an elastic object when work is done on the object.
How is momentum calculated?
Momentum (kgms^-1) = mass (kg) x velocity (ms^-1)
What happens to the momentum of two objects when they collide?
Momentum is conserved.
What does the law of conservation of momentum apply to?
A closed system.
Why does momentum have a direction as well as size?
Velocity is a vector quantity (ie. in a certain direction)
When would two objects move at different speeds when pushing away from each other?
If the objects have different masses.
When two objects push away from each other, why is their total momentum zero?
They have equal and opposite momentum.
When vehicles collide, what does the force of the impact depend on?
The mass, change of velocity, duration of the impact.
How does the impact force depend on the impact time?
The longer the time, the more the force can be reduced.
Describe the impact forces and total momentum when two vehicles collide.
- They exert equal and opposite forces on each other.
- Their total momentum is unchanged.
How are cars designed to lessen force on the passengers?
The front and rear of the cars are crumple zones increasing the impact time which reduces the impact force on the car.
How does the force of an impact change the momentum of a car?
- A front end impact reduces the momentum.
- A rear end impact increases the momentum.
Give five features that are designed to improve car safety.
- Crumple zones.
- Side impact bars.
- Seat belts.
- Airbags.
- Collapsible steering wheel.
Give two design feature benefits of seat belts.
- The decelerating force is reduced.
- The force is spread across the chest rather than the head on the windscreen.
