A fire tongs has its arms 20 cm long. It is used to lift a coal of weight 1.5 kgf by applying an effort at a distance 15 cm from the fulcrum.

Find:

(i) the mechanical advantage of fire tongs and

(ii) the effort needed.

The figure given below shows a fixed pulley used by a boy to lift a load of 200 N through a vertical height of 5 m in 10 s. The velocity ratio of the pulley is 

1. 0
2. 1
3. 2
4. none

Which of the following statements is incorrect?

1. The velocity ratio of a single fixed pulley is always 1.
2. The velocity ratio of a single movable pulley is always 2.
3. The velocity ratio of a combination of n movable pulleys with a fixed pulley is always 2ⁿ.
4. The velocity ratio of a block and tackle system is always equal to the number of strands of the tackle supporting load.

If there are n movable pulleys with one fixed pulley, the mechanical advantage is given by :

1. 2ⁿ 
2. 2ⁿ⁺¹  
3. 2^n-1
4. 2ⁿ⁺²