N02/17:write 2 equations . dsin 45 = 3 ~ & dsin 90 n~. divide one by the other. You get n = 3/sin 45. Take the lower whole number .

N2000/22:angle 0 : pr is hpg higher than atm pr. angle 90: pr is same as atm. Angle 180 :pr is hpg lower than atm. The other angles above 180 is symmetrical

N2005/12:when the temp rise , speed of molecules rise. Use first law : W is positive , Qis zero(suddenly moved no time to absorb/give out heat).hence delta U is positive . T increase .

N2000/25: rate of hear loss const. mc@/ t = mL / t2 Cancel m. C/L = 1/(@/t)(t2)

N2004/14:the content are at constant temp hence delta U = 0. no change in volume of content , W = 0. q = 0. all three zero.