## 2010年12月23日 星期四

(有動畫顯示)

wiki:

### 純滾動

$\boldsymbol{ v}_G(t) = \boldsymbol{\omega} \times \boldsymbol{R}_{G/O}\,$ ；

$v = R \omega\,$ 。

## 2010年12月3日 星期五

### Physics Chapter8-64

P.230

64. A block of mass m1 = 20.0 kg is connected to a block of mass m2 = 30.0 kg by a massless string that passes over a light, frictionless pulley. The 30.0-kg block is connected to a spring that has negligible mass and a force constant of k = 250 N/m as shown in Figure P8.64. The spring is unstretched when the system is as shown in the figure, and the incline is frictionless. The 20.0-kg block is pulled a distance h = 20.0 cm down the incline of angle q = 40.0° (so that the 30.0-kg block is 40.0 cm above the floor) and released from rest. Find the speed of each block when the 30.0-kg block is 20.0 cm above the floor (that is, when the spring is unstretched).