[填空题]
Suppose the coefficient of kinetico+0c 4lbiy o ci*8hu5s fricj bc.83,vpi vltion between $m_{1}$ and the plane in Fig. 4-57 is $ \mu_{\mathrm{k}}=0.15$ , and that $m_{1}=m_{2}=2.7 \mathrm{~kg}$ . As $m_{2}$ moves down, determine the magnitude of the acceleration of $ m_{1}$ and $m_{2}$ , given $\theta=25$ ?
(b) What smallest value of $\mu_{\mathrm{k}}$ will keep this system from accelerating?
