Work, Energy and Power

Question 1

what is the conservation of energy

Answer 1

total energy before = total energy after

Question 2

what is work

Answer 2

when energy is added to or removed from a system

Question 3

when is work done

Answer 3

work is done when a force is applied to an object and the object moves in the same direction as the applied force

Question 4

what is the formula for work

Answer 4

wd = F x s

Question 5

how do you find the work of an object at an angle

Answer 5

you use the component of force that is in the same direction as the motion

Question 6

what is the formula for work at an angle

Answer 6

W = Fscostheta

Question 7

maria walks up a 3 meter tall staircase in 15s. Paige runs up it in 5s. Who does more work

Answer 7

they do the same amount of work cos work only depends of force and distance

Question 8

what is power

Answer 8

the rate at which work is done

Question 9

what is the relationship that links power and work done

Answer 9

power = work done/time

Question 10

what average force is needed to slow a car of mass 1200kg from 30 ms-1 to 10ms-1 over a distance of 50m?

Answer 10

Wd = Fs
Wd = final ke - initial ke
Wd = 60000-540000 = -480000J
Wd/s = F = -480000/50
F = -9600N

Question 11

what is a joule in si units

Answer 11

ke = 1/2mv2
kg(ms-1)^2
= kgm2s-2

Question 12

what is a watt in si units

Answer 12

kgm2s-3

Question 13

what does the area under a force distance graph equal

Answer 13

work done

Question 14

what is hookes law formula

Answer 14

F = kx

Question 15

what is the formula for elastic potential energy

Answer 15

1/2k(delta(x))^2

Question 16

when is the elastic potential energy formula used

Answer 16

for a non-constant force

Question 17

A system that consists of a single spring stores a total elastic potential energy Ep when a load is added to the spring. Another identical spring connected in parallel is added to the system. The same load is now applied to the parallel springs. What is the total elastic potential energy stored in the changed system?

Answer 17

https://www.youtube.com/watch?v=D50iNfj-qik

Question 18

An increasing force acts on a metal wire and the wire extends from an initial length l0 to a new length l. The graph shows the variation of force with length for the wire. The energy required to extend the wire from l0 to l is E. The wire then contracts to half its original extension.

What is the work done by the wire as it contracts?

Answer 18

https://www.youtube.com/watch?v=QBEzkeuYOn4