## Chapter 1.3 - Simple Machines Exercise 28

Question 1
What is the use of a fixed pulley?
Solution 1
A fixed pulley is used to change the direction of effort to a convenient direction.
Question 2
In which direction will the force be applied when a single pulley is used with a mechanical advantage greater than unity?
Solution 2
When a single pulley is used with a mechanical advantage greater than 1, the effort has to be applied in the upward direction.

Question 3
In a single fixed pulley, If the effort moves by a distance y downwards, by what height is the load raised?
Solution 3
In a single fixed pulley, if the effort moves by a distance 'y' downwards, the load moves by a distance 'y' upwards because the velocity ratio of a single fixed pulley is 1.
Question 4
What is a single movable pulley? What is its mechanical advantage in the ideal case?
Solution 4
A pulley whose axis of rotation is not fixed in position or space is called a movable pulley. Ideally, its M.A. is 2.

Question 5
Name the type of single pulley that can act as a force multiplier. Draw a labeled diagram of the pulley mentioned by you.
Solution 5
Question 6
Give reasons for the following:
(i)    In a single fixed pulley, the velocity ratio is always more than the mechanical advantage.
(ii)    The efficiency of a pulley is always less than 100%.
(iii)    In case of a block and tackle arrangement, the mechanical advantage increases with the increase in the number of pulleys.
Solution 6

Question 7
What is an ideal machine?
Solution 7
A machine whose efficiency is 100% is referred to as an ideal machine.
Question 8
Write the relation between mechanical advantage, velocity ratio and efficiency.
Solution 8

Question 9
Can a machine be 100% efficient?
Solution 9
No, a machine cannot be 100% efficient because mechanical advantage is always less than theoretical mechanical advantage due to friction and the weight of the moving parts.
Question 10
Define velocity ratio? State its unit.
Solution 10

Question 11
What is the purpose of a machine?
Solution 11
The purpose of a machine is:
(i) To multiply force
(ii) To obtain a gain or decrease in speed
(iii) To change to direction of application of force in a convenient direction
Question 12
Give an example for each of the following uses of a machine: (i) to obtain gain in force,
(ii) to change the point of application of force,
(iii) to change the direction of force,
(iv) to obtain gain in speed.
Solution 12
(i) A jack is used to multiply force.
(ii) A lever is used to change the point of application of force.
(iii) A pulley is used to change the direction of application of force.
(iii) Gears are used to multiply speed.

Question 13
Solution 13
Question 14
What is a block and tackle system of pulleys?
Solution 14
A block and tackle system of pulleys consists of two blocks of pulleys, each block having one or more than one pulley. The upper block of pulleys is fixed to a rigid support and the lower block of pulleys is movable. The number of pulleys in the movable block is either equal to or one less than the number of pulleys in the fixed block.

## Chapter 1.3 - Simple Machines Exercise 29

Question 1
Name a machine which is used to:
(a) multiply force
(b) multiply speed
(c) change the direction of force applied.
Solution 1
(a) A jack is used to multiply force.
(b) Gears are used to multiply speed.
(c) A pulley is used to change the direction of application of force.
Question 2
Write two uses of pulleys. Is pulley a force multiplier?
Solution 2
Two uses of pulley:
(i) To change the direction of application of force to a convenient direction.
(ii) To multiply force.
Yes, a pulley is a force multiplier

Question 3
Solution 3
Question 4

Solution 4

Question 5
What is a block and tackle system of pulleys?
Solution 5
A block and tackle system of pulleys consists of two blocks of pulleys, each block having one or more than one pulley. The upper block of pulleys is fixed to a rigid support and the lower block of pulleys is movable. The number of pulleys in the movable block is either equal to or one less than the number of pulleys in the fixed block.
Question 6

Solution 6