[填空题]
1.A small ball of ma;(.lcsubv g6 f,e:l:5imo ijn;*m-0qyh/shxxv el,aie zq.1;mm k f*ss $m$ is oscillating on a frictionless curved surface.
$x$ is the horizontal displacement from the middle point $O$ of the motion. The shape of the surface is such that the relationship between net force in the horizontal axis and displacement is given by the expression
$F=-m\frac{gx}{r}$
where g is the acceleration of free-fall and r is the radius of the curvature of the surface.
Outline why the ball performs simple harmonic motion.
2.The radius r of the frictionless surface and the mass m of the ball are $10\,cm$ and $20\,g$ respectively.
(1)Show that $ω=\sqrt{\frac{g}{r}}$
(2)Calculate, in $s$, the time taken for the ball to reach point $O$ after being released from the highest point.The time needed for the motion= s
(3)Draw, on the axes, the graph to show how the kinetic energy of the ball varies with displacement during its motion from the start until it reaches point $O$. Be sure to include the values for the vertical and horizontal intercepts.
