Q1: What is the mechanical advantage of a Class II lever? (a) Always less than 1 (b) Always equal to 1 (c) Always greater than 1 (d) Can be greater than, equal to, or less than 1
Solution:
Ans: (c) Explanation: In a Class II lever, the load is between the fulcrum and effort. The effort arm is always longer than the load arm, making M.A. always greater than 1.
Q2: Which simple machine is formed by wrapping an inclined plane around a rod? (a) Pulley (b) Wedge (c) Screw (d) Wheel and axle
Solution:
Ans: (c) Explanation: A screw is an inclined plane wrapped around a rod with spiral threads. It helps hold things together or lift heavy objects with less effort.
Q3: In which class of lever is the effort located between the fulcrum and the load? (a) Class III lever (b) Class I lever (c) Class II lever (d) All classes of levers
Solution:
Ans: (a) Explanation: In a Class III lever, the effort is positioned between the fulcrum and the load. This makes it a speed multiplier with M.A. less than 1.
Q4: What is the mechanical advantage of a fixed pulley? (a) Less than 1 (b) Equal to 1 (c) Greater than 1 (d) Equal to 2
Solution:
Ans: (b) Explanation: A fixed pulley is attached to a hook or wall and does not move. Its mechanical advantage is equal to 1, meaning applied force equals load weight.
Q5: Which simple machine is made by combining two inclined planes joined together? (a) Lever (b) Screw (c) Pulley (d) Wedge
Solution:
Ans: (d) Explanation: A wedge is usually made of two inclined planes joined together. It has slanting sides that meet at a sharp edge for cutting or splitting objects.
Fill in the Blanks
Q1: The fixed point around which a lever moves is called the _____.
Solution:
Ans: fulcrum
Q2: The distance between two threads on a screw is called its _____.
Solution:
Ans: lead
Q3: A machine that combines two or more simple machines is called a _____ machine.
Solution:
Ans: complex
Q4: The unit of energy is named after James Prescott Joule and is called _____.
Solution:
Ans: joule
Q5: An arrangement of multiple pulleys together is called a _____ system.
Solution:
Ans: block and tackle
True or False
Q1: No machine has 100% efficiency because some energy is always lost as heat due to friction.
Solution:
Ans: True Explanation: All real machines lose some energy as heat from friction between parts. A machine with 100% efficiency is only an ideal, theoretical concept.
Q2: In science, work is done even when an object does not move after applying force.
Solution:
Ans: False Explanation: Work happens only when a force moves an object in the direction of the force. If the object doesn't move, no work is done.
Q3: A Class I lever always has a mechanical advantage greater than 1.
Solution:
Ans: False Explanation: A Class I lever can have M.A. greater than 1, equal to 1, or less than 1, depending on the positions of effort and load arms.
Q4: The longer the inclined plane, the easier it is to move the load but it takes more time.
Solution:
Ans: True Explanation: A longer inclined plane requires less effort to move a load upward, but the distance travelled increases, which takes more time to complete.
Q5: A wheel and axle can only act as a force multiplier.
Solution:
Ans: False Explanation: A wheel and axle can act as both a force multiplier and a speed multiplier, depending on how force is applied to it.
Match the Following
Column A
Column B
1. Crowbar
A. Class III lever
2. Wheelbarrow
B. Wheel and axle
3. Fishing rod
C. Inclined plane
4. Doorknob
D. Class I lever
5. Ramp for wheelchair
E. Class II lever
Solution:
Ans:
1 - D: A crowbar is a Class I lever where the fulcrum is between effort and load, changing the direction of force applied.
2 - E: A wheelbarrow is a Class II lever where the load is between fulcrum and effort, making it a force multiplier.
3 - A: A fishing rod is a Class III lever where effort is between fulcrum and load, acting as a speed multiplier.
4 - B: A doorknob is a wheel and axle where the knob is the wheel and the rod inside is the axle.
5 - C: A ramp for wheelchair is an inclined plane that helps move people up or down with less effort.
Short Answer Questions
Q1: What is a lever and how does it help us do work?
Solution:
Ans: A lever is a rigid bar or rod that moves around a fixed point called the fulcrum. It is used to lift heavy weights with less effort. The point where effort is applied is the effort arm, and the point where load is lifted is the load arm. Examples include hammers, tongs, scissors, and pliers. Levers make work easier by changing force direction or multiplying force applied.
Q2: Explain the difference between a fixed pulley and a movable pulley.
Solution:
Ans: A fixed pulley is attached to a hook or wall and does not move but changes the direction of force. Its mechanical advantage is equal to 1, meaning applied force equals load weight. A movable pulley moves with the load and reduces the effort needed to pull it. Its mechanical advantage is less than the load weight. Examples include well pulleys and cranes respectively.
Q3: Why is no machine 100% efficient? Explain with an example.
Solution:
Ans: No machine has 100% efficiency because some energy is always lost as heat due to friction between moving parts. For example, a petrol engine has about 50% efficiency, meaning only 50% of petrol energy turns into useful work and the rest is lost. A machine with 100% efficiency is called an ideal machine, but this is impossible in real life.
Q4: What is an inclined plane and how does it make work easier?
Solution:
Ans: An inclined plane is a sloping surface that connects two points at different heights. It helps move heavy objects up or down with less effort. The longer the inclined plane, the easier it is to move the load, but it takes more time. If the slope is steeper, more effort is needed. Examples include children's slides, ramps for wheelchairs, and sloping roads.
Q5: How does a screw work as a simple machine? Give examples.
Solution:
Ans: A screw is an inclined plane wrapped around a rod with spiral threads. The threads grip material tightly, helping hold things together or lift heavy objects. The distance between two threads is called its lead. If the lead is small, the screw gives more mechanical advantage. It acts as a force multiplier. Examples include bolts, screws, jar caps, and screw jacks used to lift cars.
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