Simple Machines (Chapter # 09) Physics 10th -Question Answers

 Physics 10th - Simple Machines

Q.1: Define Machine. Write Down the Useful Purposes of Machines.

Ans: Machine: A machine is a device used to perform work in a more convenient way or to speed up work.

OR

A machine can be defined as any device that uses force applied at one point to overcome resistance at another point.

Useful Purposes of Machines:

1. To lift heavy loads.
2. To increase the rate of doing work.
3. To change the direction of force.
4. To transfer energy from one point to another.

Q.2: Define the Following Terms:

• Effort
• Load
• Input
• Output

Ans:

• Effort (P):
  A force directly applied to a machine is called effort. It is denoted by $P$. Its unit is Newton, and it is a vector quantity.

• Load (W):
  A resistance overcome by a machine is called load. It is denoted by $W$. Its unit is Newton, and it is a vector quantity.

• Input:
  The work done on a machine by the effort. It is the useful energy supplied to the machine, calculated as:

  $$\text{Input} = \text{Effort} \times \text{Effort Arm}$$ $$\text{Input} = P \times d$$

OUTPUT:
The useful work done by the machine on the load is called output. So, the output of the machine is given by:

$\text{Output} = \text{load} \times \text{load arm}$
$\text{Output} = W \times h$

Q.3: Define mechanical advantage?
Ans: The ratio between the load lifted and the effort applied is called the mechanical advantage of a machine.

If "W" is the weight lifted by the machine and "P" is the effort applied to the machine, then

$$\text{Mechanical Advantage} = \frac{\text{Weight lifted by the machine}}{\text{Effort applied}}$$ $$\text{M.A} = \frac{W}{P}$$

The M.A is a ratio between two forces, so it has no unit. It is expressed in numbers.

Q.4: Define efficiency? Write down its formula.
Ans: The ratio between the useful work done by the machine (output) to the work done on the machine (input) is called efficiency.

$$\text{Efficiency} = \frac{\text{Useful Work done by the machine}}{\text{Work done on the machine}}$$ $$\eta = \frac{\text{Output}}{\text{Input}}$$ $$\eta = \frac{W \times h}{P \times d}$$

Efficiency is usually expressed in percentage:

$$\eta = \frac{W \times h}{P \times d} \times 100$$

The efficiency of a real machine is always less than 1. A perfect machine has 100% efficiency or 1. For an ideal machine,

$$\text{Efficiency} = \eta = 1$$ $$\frac{\text{Output}}{\text{Input}} = 1$$

So,

$$\text{Input} = \text{Output}$$

Q.5: Write down the kinds of machines?
Ans: In our daily life, we use different kinds of machines as under:

• Lever
• Inclined plane
• Screw
• Screw jack
• Wedge
• Wheel and axle

Q.6: Define lever? Find its mechanical advantage?
Ans: MS. LEVER:
A lever is a rigid bar which rotates about a fixed point called fulcrum.

Mechanical Advantage:
By applying force at one end of a bar, weight can be lifted at the other end. The perpendicular distance between force and fulcrum is called force arm or effort arm, and the perpendicular distance between fulcrum and weight is called weight arm or load arm.

The turning effect of any force is called torque, which is equal to the product of force and perpendicular distance. If the two torques are equal, then the lever is said to be in equilibrium.

Diagram:
A diagram shows a lever with the following labels:

• Weight arm (C to B)
• Effort arm (B to A)
• Centre of gravity
• Fulcrum

Principle of Lever:
When a lever is in equilibrium, then:

$$\text{Torque of the effort} = \text{Torque of the load}$$ $$\text{Effort} \times \text{effort arm} = \text{Load} \times \text{load arm}$$

From the figure:

$$P \times m \text{AB} = W \times m \text{BC}$$