friction
${\operatorname{mr} \omega^{2} \geq \mu m g} $
${r \omega^{2} \geq \mu g}$
$\mathrm{r} \omega^{2} \geq \mathrm{constant}, \mathrm{or}\left(\frac{\mathrm{r}_{1}}{\mathrm{r}_{2}}\right)=\left(\frac{\omega_{2}}{\omega_{1}}\right)^{2}$
$\frac{4 \mathrm{cm}}{\mathrm{r}_{2}}=\left(\frac{2 \omega}{\omega}\right)^{2} \quad \therefore \mathrm{r}_{2}=1 \mathrm{cm}$
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$[1]$ The graph of kinetic energy $E_k$ of the ball against height $h$ is shown in figure $1$
$[2]$ The graph of height $h$ against time $t$ is shown in figure $2$
$[3]$ The graph of gravitational energy $E_g$ of the ball against height $h$ is shown in figure $3$
Which of $A, B, C, D, E$ shows the correct answers?