Forces and energy Flashcards
Define work done and give the equation to work it out
When a force causes an object to move through a distance. Equivalent to energy transferred work done (W, J) = force (F, N) x distance in the direction of the force (d, m)
Describe the re-entry of a shuttle from space into earth, in terms of work done and energy
The force is very great because the shuttle has a high mass and is accelerating (F=ma). The distance is also very long. This means the work done is great, which means lots of energy is transferred as heat, light and sound (hence the plasma around it)
Define power and give an equation linking it to energy transfer/work done and time
Power is the work done/energy transferred in a given time
P = E/t [P is in Watts, w; E is in joules, J; time is in seconds, s)
Define gravitational potential energy and give an equation linking it to mass, gravitational field strength and height
The energy an object has by virtue of its position in a gravitational field
(Δ)GPE = m x g x (Δ)h
Define kinetic energy and give an equation linking it to mass and speed
The kinetic energy (KE) of an object depends upon its mass and its speed
KE = 1/2 x m x v^2
Give an equation linking momentum to mass and velocity
p = m x v [momentum, p is in kilograms metres per second, Kgm/s]
Define conservation of momentum and explain why a gun recoils in these terms
In a closed system the total momentum before an event is equal to the total momentum after the event
A gun fires a bullet with a high velocity but low mass giving (-ve) momentum (mv). Momentum before the event was 0, so must it be afterwards. Gun recoils with (+ve) momentum, cancelling out momentum.
