ok....tutor showed me
volume of the stripe is 5 x sqrt(2^2 - y^2) x dy
distance is (5-y)
integral from -2 to 2
weight of gasoline is 42
so 42(5)(integ -2 to 2) (5-y)(sqrt(2^2 - y^2))dy
=210(integ -2 to 2) (5-y)(sqrt(2^2 - y^2))dy
i got 420(integ -2 to 2) (5-y)(sqrt(2^2 - y^2))dy
so the only thing i had different was is that my constant in front of the integral is double his.
i think what i got was 42(5)(2). the 2 coming from (2)sqrt(2^2 - y^2) because its the radius, so you need to double it in order to get the length/diameter of the strip.
i dont know who is right though...i wish i had written down all my steps when i did this on the exam....