Short/long answer questions( Q1 -Q12 )of chapter 4 (based on simple machines) of class 6.

 1. When is work said to be done by a force?

Ans. A work is said to be done by a force when a body is displaced or moves in the direction of force applied.

2. What is energy?

Ans. Energy  is the capacity or ability of a body to do work.

3. What do you understand by a machine?

Ans.machine is a device which acts as a force multiplier or speed multiplier allowing us to apply effort at a more convenient point in and easier direction.

4. What is the principle on which a machine works?

Ans. No machine work of its own. When energy is supplied to it, it does some useful work. Work done on the machine is called as work input and work done by the machine is called as work output.

5. State two functions of a machine.

Ans. Two functions of a machines are as follows:

1. Acts as a force multiplier

2. Acts as a speed multiplier

6. Name six simple machines. Give an example of each machine.

Ans. Six simple machines are as follows:

1. The lever example Mango cutter, beam balance, a pair of scissors, etc.

2. The pulley eg.pulley is used in well to draw water from it,to lift heavy load in factories etc.

3. The wheel and axle example door knob, steering wheel, etc.

4. The incline plane example staircase , ramp etc.

5.The wedge example of needle,axe,etc.

6.The screw.eg. fixing hinge in door & windows,attaching lock in the door etc.

7. Define the term 'work output'and'work input'in relation to a machine.

Ans. Work output  is the usefull work done by the machine on the load.

Work input is the work done on the machine by the effort.

8. Explain the term mechanical advantage of a machine.

Ans. The mechanical advantage of a machine is the ratio of the load to the effort. Or

the factor by which machine multiplies the force applied is called the mechanical advantage.

In words it can be written as,

Mechanical advantage=load/effort

1.If mechanical advantage of a machine is greater than 1 then it acts as a force multiplier.

2.if mechanical advantage of a machine is less than 1 then it acts as a speed multiplier.

3.if mechanical advantage of a machine is equal to 1 then it acts as a direction changer or to apply effort at a more convenient point in a convenient direction.

9. Define the term efficiency of a machine.

Ans.the efficiency of a machine is the ratio of the useful work done by the machine to the work you put into the machine by the effort.

Efficiency=work output on load/work input by effort.

10. What is an ideal machine?

Ans. Ideal machine is a machine in which no part of the work done on the machine is wasted. For an ideal machine, the work output is equal to the work input. The efficiency of an ideal machine is 100%.

11. Can a machine have an efficiency of 100%? Give reason to support your answer.

Ans. No .

Machinec have an efficiency of 100% because some part of the work done on a machine is always wasted in overcoming the friction between the moving parts of the machine.

12. 'A machine is 75% efficient'. What do you understand by this statement?

Ans. If a machine is 75% efficient,it means that 75% of the work input to the machine is obtained as the useful work output. The remaining 25% of the work input has been wasted in overcoming the friction.