Class 9 ch 10 Work and Energy
Class 9 ch 10 Work and Energy
**1. What are the two essential conditions for work to be done?**
A force must act on an object, and the object must be displaced.
**2. How is work defined scientifically when a constant force is applied?**
Work done is equal to the product of the magnitude of the force and the distance moved in the direction of the force ($W = F \times s$).
**3. What is the SI unit of work and energy?**
The unit of work and energy is the joule (J), which is equivalent to one newton-metre (1 N m).
**4. When is the work done by a force considered to be negative?**
Work done is negative when the applied force acts in the opposite direction of the object's displacement.
**5. How is "energy" defined in science?**
Energy is an object's capability or capacity to do work.
**6. What is kinetic energy?**
Kinetic energy is the energy possessed by an object due to its motion, and it is calculated using the formula $E_k = \frac{1}{2}mv^2$.
**7. What is potential energy?**
Potential energy is the energy present in an object by virtue of its position, shape, or configuration.
**8. What is the formula for the gravitational potential energy of an object raised to a height?**
The gravitational potential energy is calculated as $E_p = mgh$, where $m$ is mass, $g$ is acceleration due to gravity, and $h$ is height.
**9. What does the law of conservation of energy state?**
It states that energy can only be transformed from one form to another; it can neither be created nor destroyed, meaning the total energy always remains constant.
**10. What is mechanical energy?**
Mechanical energy is the sum of the kinetic energy and potential energy of an object.
**11. What is power?**
Power is defined as the rate of doing work or the rate of transfer of energy ($P = \frac{W}{t}$).
**12. What is the SI unit of power?**
The SI unit of power is the watt (W), where 1 watt equals 1 joule per second ($1 \text{ J s}^{-1}$).
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