21. Draw diagrams to illustrate the positions of fulcrum load and effort in each of the following:
a) see-saw - figure 4.8 a.
b) beam balance-figure 4.8 d
c) a nutcracker -figure 4 .10 a
d) a pair of forceps- figure 4.12 d
22. How can you increase the mechanical advantage of a lever?
Ans. Mechanical advantage of a lever can be increased in following ways:
a) by increasing the effort arm and decreasing load arm.
b) by reducing the friction at the fulcrum of a lever.
23. How does the friction of the forum affect the mechanical advantage of the lever?
Ans. The friction at the fulcrum, increases the mechanical advantage of the lever.
24. State three differences between three classes of the levers.
Ans.write from page no.55. distinction between the three classes of levers.
25. What is a pulley?
Ans.a pulley is a simple machine which is used for raising a load up by applying the effort downwards.
26. What is the mechanical advantage of an ideal pulley?
Ans. The mechanical advantage of an ideal pulley is 1 or 100%.
27. The mechanical advantage of an actual pulley is less than 1. Give reason. What is a justification for using the pulley then??
Ans. The mechanical advantage of an actual pulley is less than 1. The reason for less than one is is because of friction between the rope and the pulley.
pulley is not used as a force multiplier but it is used for changing the direction of the effort. To apply I the effort in a more convenient direction that is in downward direction.
28. Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Ans. Figure 4.14 of your physics book.
In an ideal situation, effort is equal to load.
29. What is an inclined plane? What is its mechanical advantage? Give two examples where it is used.
Ans. An inclined plane is a simple machine which is used to move a load up with a less effort. It is a sloping or slanting surface.
The mechanical advantage of an inclined plane is always greater than 1.
Two examples of incline plane are as follows:
a) the staircase in our house.
b) the roads on a hill are made in inclined with a small slope.
30. What is a screw? Give two examples.
Ans. Screw is a simple machine which appears like an incline plane wound around a rod with a pointed tip. It is a modified form of an inclined plane.
Following are the two examples of A screw:
a) screw is used to fix a door through hinge.
b) screw Jack is a simple machine which is used to lift heavy vehicles such as car, trucks, buses etc.
31. What is wheel and axle? Give two examples.
Ans.the wheel and axle is a simple machine having a wheel and an axle. the linear motion of axle is obtained by rotating the wheel so as to reduce friction.
Following are the two examples of wheel and axle:
a) steering wheel
b) screw driver.
32. How does a wheel help in moving the axle?
Ans.A wheel help in moving the axlel by reducing the frictional force.Because rolling friction is less than the sliding friction.
33. What is a wedge? Give two examples.
Ans. A wedge is a sharp edge formed by joining two inclined planes together to form a sharp edge which is used to split a log.
The two examples of a of a wedge are:
a) nail\knife
b) needle\axe.
34. Name the machine to which the following belong:
a) beam balance-class 1 lever
b) lemon crusher- class 2 lever
c) sugar tong- class 3 lever
d) ramp- an inclined plane
E) door knob- wheel and axle
f) needle- wedge
35. What care would you take to increase the lifespan of a machine which you use?
Ans. Following cares we should take to increase the lifespan of a machine:
a) machine machine should be kept clean and free from dust particles.
b) it should be prevented from getting rusted. By painting it with paint from time to time.
c) to reduce friction of the moving parts of a machine, moving parts must be properly lubricated from time to time.
36. Select the correct statement:
a) A wheel barrow is a lever of class 1.
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 a load vertically up then to push it along an inclined plane.
f) screw is made by two inclined planes placed together.
Ans.c) friction in moving parts of a machine reduces its efficiency.
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