Work And Energy Flashcards
When a force acts on a moving body, what happens to energy? (2)
It is transferred, but the total amount of energy remains constant.
What is the equation for work done?
Work done (J) = force (N) x distance moved in the direction of the force (m)
What is work a measure of? (2)
The energy transfer. Work = energy transfer (in the absence of thermal transfer)
Has work been done if there is no motion in the direction of the force?
No (unless it is a resistive force such as friction that acts in the opposite direction to movement)
What energy is possessed by an object in motion?
Kinetic
How does an object posses gravitational potential energy?
Because of its position
What energy does an object possess because of deformation?
Elastic energy
Equation for kinetic energy?
KE (J) = 1/2 x mass (kg) x velocity*squared (m/s)
Equation for gravitational potential energy?
PE = mass (kg) x gravitational field strength (n/kg)or(m/s2) x change in height (m)
What is the relationship between force and extension for a spring?
force (N) = spring constant (N/m) x extension (m),
F =kx
How do you calculate the work done in stretching a spring using a graph?
Find the area under the force extension graph (W=1/2Fx for a linear relationship
How do you calculate the extensions of a spring?
The final length of the spring - the initial length of the spring
How can energy efficiency of vehicles be improved? (4)
by:
- reducing aerodynamic losses/air resistance
- reducing rolling resistance
- idling losses
- inertial losses
How can aerodynamic losses/air resistance be reduced in vehicles?
more streamlined designs.
How can rolling resistance be reduced in vehicles? (2)
having correctly inflated tyres and using materials which don’t heat up as much as they are squashed.
How can idling losses be reduced in vehicles?
by using stop - start systems
How can inertial losses be reduced in vehicles?
by having lighter cars.
why is it important to improve the efficiency of vehicles (2)?
- so less energy is used for a journey to reduce the cost
- to use less energy so that less fossil fuels are burned for energy, improving the environment
when is the force applied to a spring not directly proportional to the extension of a spring?
After the elastic limit has been exceeded.
What safety features are present in cars? (2)
- airbags
- crumple zones
How does an airbag make a person safer in the event of a head-on collision? (6)
- It deploys in front and to the sides of a passenger during a collision
- to increase the distance that the occupant travels before coming to a rest
- The kinetic energy of the occupant is reduced to zero by work being done on the person
- Work is the product of force and distance,
- so by increasing the stopping distance, the force is reduced
- This results in less chance of an injury
