A car is going at a speed of 6m/s when it encouters a 15 m slope of angle $30 ^{\circ}$. The frictional coefficient between road and tyre is 0.5. The driver applies the brakes. The minimum speed of car with which he can reach the bottom is $(g=10 m/s^2)$

Question

$$(a)\;4\;m/s \quad (b)\; 3\;m/s \quad (c)\; 8.45 \;m/s \quad (d)\;7.46\;m/s$$