A-LEVEL PHYSICS: 4.7.6: Energy Conservation (SaveMyExams)

Question 1

what happens when a metal wire is loaded with a force & stretched beyond its limit of proportionality?

what happens when the force is removed?

Answer 1

undergo plastic deformation

wire is unloaded, causing the extension to decrease

Question 2

explain the features of the force-extension graph of a material that has undergone plastic deformation: (3)

Answer 2

-unloading line parallel to loading line (since k is constant)

-unloading line does not go through origin (since there is still some extension after unloading the force(plastic deformation))

-area between loading & unloading lines represents work done to permanently deform the wire

Question 3

force-extension graph for a material may not always be the same when ___ & ___

Answer 3

loading, unloading

Question 4

explain the features of force-extension graph for stretching & contracting a rubber band: (5)

Answer 4

-loading (up) & unloading curves (down)

-unloading (contraction) curve goes through origin (since no extension once force is removed)

-area between 2 curves: work done in heating the rubber

-area under unloading curve: work done in stretching the rubber band

-total area under loading curve: total work done

Question 5

what does the force-extension graph for stretching & contracting a rubber band show overall?

Answer 5

rubber band stores a greater amount of strain energy when it is loaded (stretched) than when its being unloaded (contracted)

Question 6

rubber band becomes warm when it is stretched and contracted hence ∴ …

Answer 6

some energy is transferred to heat energy

Question 7

car shock absorbers:

Answer 7

-elastic objects

-designed to absorb impact