Question

suppose a roller coaster passes point 1 with a speed of 1.7m

Answer 1

重力与摩擦力所做的功等于动能的增量

mgh1-mg*1/15*s=1/2mv^2-1/2mv0^2

v2=[2(1/2mv^2+mgh1-mg*1/15*s)/m]^0.5

=[2(1/2x1.7x1.7+10x35-10x1/15x45)]^0.5

=25.4m/s

It will reach point 2 with a speed of 25.4m/s

The 2rd question I do not know.