Help needed

[onur369]

Hey guys theres this one question that is constantly bugging me. I keep using the us=0.5kx^2 but it wont work.

Question 26 of attachment

[xZero]

at the first linear part,
f=-kx
700=0.3k
k=7000/3
E=0.5kx^2
E=105J

2nd part
f=-kx
100=0.2k
k=500
E=0.5kx^2
E=10J

total energy=10+105=115J

im not too sure about this 1, need some1 to verify

[onur369]

The answer is 13J

[Respect]

yeah, this question was retarted. for the first answer, i got 50cms, becuase it u look at the graph is sorta makes no sence, but if u read carefullly the question says it applies a stopping force of 800N ... so look on the graph, 800N and on the x-axis (compression) its 50 .. so 50 cm

 but for 26, the energy stored is suppose to be the area under the graph, according to the "cheat sheet' ..

buut my area was something like

area of trapizum, A= 0.5 (700+800) x (20x10^(-2)  = 15
area of trianghle A=((30x10^-3) x 700 ))divided by two. = 10.5
add them together, add them together i got 25.5

then where did they get the 13 .. abbas knows.