Selina solutions concise physics class 6 icse Solutions for Chapter 4 simple machines

Q1) In a mechine an effort of 10 kgf is applied to lift a load of 100 kgf. What is its mechanical advantage?

Q2) The mechanical advantage of a machine is 5. How much load it can exert for the effort of 2kgf?

Q3) The mechanical advantage of a machine is 2. It is used to raise a load of 15 kgf. What effort is needed?

Q4) A lever of length 100 cm has effort of 15 kgf at a distance of 40 cm from the fulcrum at one end. What load can be applied at its other end?

Q5) In a lever, fulcrum is at one end at a distance of 30 cm from the load and effort is at th other end at a distance of 90 cm from the load. Find:

1. the length of load arm
2. the length of effort arm
3. the length mechanical advantage of the lever

Q1) State whether the following statements are True or False.

1. A boy does work while pushing a wall

2. A machine performs work by itself

3. In an ideal machine, work done on load is equal to the work done by effort

4. All levers are force multipliers

5. A pulley changes the direction of force

6. An inclined plane always has the mechanical advantage more than 1

Q2) Fill in the blanks

1. The useful work done by an actual machine is always____ than the work done on the machine.

2. In class II levers, the load is in between fulcrum and ____.

3. The mechanical advantage of class ______ lever is always less than 1.

4. A pulley is used to change ______.

5. The mechanical advantage of an inclined plane is always______.

Q3) Match the following

Q4) Select correct alternative

(a) For an ideal machine, the efficiency is

1. Greater than unity

2. Less than unity

3. Equal to unity

4. Depends on the value of load

(b) Mechanical advantage of a machine is define as

1. Load x effort

2. Load / effort

3. Load + Effort

4. Effort / Load

(c) The mechanical advantage of a lever is equal to

1. Load arm / effort arm

2. Effort arm/ load arm

3. Load arm + effort arm

4. Load arm – effort arm

(d) A pulley is used because it

1. Has the mechanical advantage greater than one

2. Has 100% efficiency

3. Helps to apply the force in a convenient direction

4. Requires more effort to raise a less load.

(e) Wheel is used with axle because

1. Sliding friction is less than the sliding friction

2. Rolling friction is less than the sliding friction

3. They work as the inclined plane

4. They help us to change the direction of force.

Q1) When is work said to be done by a force?

Q2) What is energy?

Q3) What do you understand by a machine ?

Q4) What is the principle on which a machine works ?

Q5) State two functions of a machine.

Q6) Name six simple machines. Give an example of each machine.

Q7) Define the term ‘work input’ and ‘work output’ in relation to a machine.

Q8) Explain the term mechanical advantage of a machine.

Q9) Define the term efficiency of a machine.

Q10) What is an ideal machine?

Q11) Can a machine have an efficiency of 100%? Give a reason to support your answer

Q12) A machine is 72% efficient. What do you understand by this statement ?

Q13) What is a lever?

Q14) Describe three orders of levers giving an example of each. Draw neat diagrams showing the positions of fulcrum, load and effort in each kind of lever.

Q15) What do you mean by the mechanical advantage of a ‘lever’?

Q16) Which class of lever has the mechanical advantage always more than 1? Give an example.

Q17) Which class of lever has the mechanical advantage always less than 1? Give an example

Q18) Give one example of class 1 lever in each case where the mechanical advantage is

1. more than 1

2. equal to 1

3. less than 1

Q19) Name the class to which the following levers belong :

1. A pair of scissors

2. A lemon squeezer

3. A nut cracker

4. A pair of sugar tongs

5. A beam balance

6. An oar rowing a boat

7. A wheel barrow

8. A see saw

9. a pair of pilers

10. a crow bar

Q20) Ther diagram given below shows the three kinds of levers. Name the class of each lever and give one example of each class

Q21) Draw diagrams to illustrate the positions of fulcrum, load and effect in each of the following

a) a see saw

b) a beam balance

c) a nut cracker

d) a pair of forceps

Q22) How can you increase the mechanical advantage of a lever?

Q23) How does the friction at the fulcrum affect the mechanical advantage of the lever?

Q24) State three differences between the three classes of levers

Q25) What is a pulley?

Q26) What is the mechanical advantage of an ideal pulley?

Q27) The mechanical advantage of an actual pulley is less than 1. Give a reason. What is the justification for using the pulley then?

Q28) Draw a neat and labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?

Q29) What is an inclined plane? What is its use? Give two examples where it is used.

Q30) What is a screw? Give two examples

Q31) What is wheel and axile? Give two examples

Q32) How does a wheel help in moving the axle?

Q33) What is a wedge? Give two examples.

Q34) Name the machine to which the following belong:

1. Beam balance
2. Lemon crusher
3. Sugar tongs
4. Ramp
5. Doorknob
6. Needle

Q35) What care would you take to increase the life span of a machine which you use?

Q36) Select the correct statement:

(a) A wheel barrow is a lever of class I.

(b) The efficiency of a machine is always 100%.

(c) Friction in moving parts of a machine reduces its efficiency.

(d) No lever has the mechanical advantage greater than 1.

(e) It is easier to lift vertically up than to push it along an inclined plane.

(f) A screw is made by two inclined planes placed together.