What is a single movable pulley? What is its mechanical advantage in the ideal case?

Give two reasons why the efficiency of a single movable pulley is not 100%.

In a single movable pulley, if the effort moves by a distance x upwards, by what height is the load raised?

Give reasons for the following —

(a) In a single movable pulley, the velocity ratio is always more than the mechanical advantage.

(b) The efficiency of a movable pulley is always less than 100%.

(c) In case of a block and tackle system, the mechanical advantage increases with the increase in the number of pulleys.

(d) The lower block of a block and tackle pulley system must be of negligible weight.