✔ 最佳答案
1. The block is initial at rest. When the angle of inclination is gradually increased from zero, the weight component mg.sin(θ) is balanced by the frictional force, which acts opposite to the the weight component. As the angle of inclination θ is further increased, the frictional force increases accordingly unitl the maximum frictional force is reached. After which, further increase of θ would cause the block to slide downward.
Therefore, before the maximim friction is reached, the net force acting on the block is zero.
2. If we take the upward direction as +ve, then the acceleration of the block is -ve (i.e. pointing downward along the slope) for both upward and downward journeys.
The motion follows the equation: v = u - at
where u is the projection velocity of the block, t is the time
The velocity-time graph is thus a straight line with slope -a, y-intercept at y = u and x-intercept at t = u/a
The graph shows that the velocity of the block decreases linearly with time until zero at the highest point. This occurs at t = u/a. After then, the block slides down with velocity increases linearly with time.
