In an experiment, a boy plots a graph between ${\left(v_{\max }\right)}^2$ and ${\left(a_{\max }\right)}^2$ for a simple pendulum for different values of (small) amplitudes, where $v_{\max }$ and $a_{\max }$ is the maximum velocity and the maximum acceleration respectively. He found the graph to be a straight line with a negative slope, making an angle of $30°$ when the experiment was conducted on the earth surface. When the same experiment was conducted at a height $h$ above the surface, the line was at an angle of $60°$. The value of $h$ is [radius of the earth = $R$]