Why are mountain roads generally made winding upwards rather than going straight up?

Given $M_1 = 10 \ kg$,$M_2 = 5 \ kg$,$\theta = 30^o$,and $g = 10 \ m/s^2$. What is the acceleration of the system?

Two blocks of equal masses are tied to the ends of a light string. The string passes over a massless pulley fixed on a frictionless surface as shown in the figure. The acceleration of the centre of mass of the blocks is ($g$ = acceleration due to gravity).

The acceleration of the system of two bodies over the wedge as shown in the figure is ....... $m/s^2$. (Take $g = 10 \ m/s^2$)

$A$ body of mass $10 \ kg$ moves a distance of $10 \ m$ with a constant velocity on a smooth inclined plane of angle $\theta = 30^\circ$. Calculate the work done by the force acting on the body in $J$. $[g = 10 \ m/s^2]$

Two masses $M_1$ and $M_2$ are arranged as shown in the figure. Let '$a$' be the magnitude of the acceleration of the system. If the mass of $M_1$ is doubled and that of $M_2$ is halved,then the new acceleration of the system is (Treat all surfaces as smooth; masses of pulley and rope are negligible).