Work Energy Extra Questions for Class 9

When studying physics, it is essential to practice solving various problems to better understand the concepts. In this blog post, we will explore some extra questions related to work and energy specifically designed for Class 9 students. These questions will help you reinforce your knowledge and prepare for exams. So, let’s dive in!

Table of Contents

• Question 1: Calculating Work Done
• Question 2: Potential Energy Calculation
• Question 3: Calculating Kinetic Energy
• Question 4: Conservation of Mechanical Energy

Question 1: Calculating Work Done

A body of mass 5 kg is lifted vertically upwards to a height of 10 meters. Calculate the work done against gravity.

To solve this question, we can use the formula:

Work Done (W) = Force (F) x Distance (d)

The force acting against gravity is the weight of the body, which is given by:

Weight (w) = Mass (m) x Acceleration due to gravity (g)

Substituting the given values:

Mass (m) = 5 kg

Distance (d) = 10 m

Acceleration due to gravity (g) = 9.8 m/s²

Let’s calculate the force:

Weight (w) = 5 kg x 9.8 m/s² = 49 N

Now, plug in the values of force and distance into the work done formula:

Work Done (W) = 49 N x 10 m = 490 J

Therefore, the work done against gravity is 490 Joules (J).

Question 2: Potential Energy Calculation

A spring with a spring constant of 100 N/m is stretched by 0.5 meters. Calculate the potential energy stored in the spring.

The potential energy stored in a spring is given by the formula:

Potential Energy (PE) = (1/2) x Spring Constant (k) x (Stretched Length (x))²

Substituting the given values:

Spring Constant (k) = 100 N/m

Stretched Length (x) = 0.5 m

Let’s calculate the potential energy:

Potential Energy (PE) = (1/2) x 100 N/m x (0.5 m)² = 12.5 J

Therefore, the potential energy stored in the spring is 12.5 Joules (J).

Question 3: Calculating Kinetic Energy

A car of mass 1000 kg is moving with a velocity of 20 m/s. Calculate its kinetic energy.

The kinetic energy of an object is given by the formula:

Kinetic Energy (KE) = (1/2) x Mass (m) x (Velocity (v))²

Substituting the given values:

Mass (m) = 1000 kg

Velocity (v) = 20 m/s

Let’s calculate the kinetic energy:

Kinetic Energy (KE) = (1/2) x 1000 kg x (20 m/s)² = 200,000 J

Therefore, the kinetic energy of the car is 200,000 Joules (J).

Question 4: Conservation of Mechanical Energy

A ball of mass 0.2 kg is dropped from a height of 5 meters. Calculate its velocity just before hitting the ground, assuming no energy is lost due to air resistance.

By applying the law of conservation of mechanical energy, we know that the initial potential energy is equal to the final kinetic energy. The potential energy of an object is given by the formula:

Potential Energy (PE) = Mass (m) x Acceleration due to gravity (g) x Height (h)

Substituting the given values:

Mass (m) = 0.2 kg

Acceleration due to gravity (g) = 9.8 m/s²

Height (h) = 5 m

Let’s calculate the potential energy:

Potential Energy (PE) = 0.2 kg x 9.8 m/s² x 5 m = 9.8 J

Since the potential energy is converted into kinetic energy, we can use the kinetic energy formula to find the velocity:

Kinetic Energy (KE) = (1/2) x Mass (m) x (Velocity (v))²

Substituting the values of potential energy and mass:

9.8 J = (1/2) x 0.2 kg x (Velocity (v))²

Moving ahead:

(Velocity (v))² = (2 x 9.8 J) / 0.2 kg = 98 m²/s²

Taking the square root of both sides:

Velocity (v) = √(98 m²/s²) ≈ 9.9 m/s

Therefore, the velocity of the ball just before hitting the ground is approximately 9.9 m/s.

Practicing these extra questions will enhance your understanding of work and energy concepts. Remember to analyze the given information, choose the appropriate formulas, and apply them to solve the problems systematically. Physics can be complex, but with practice, it becomes easier to tackle.

For further assistance and to dive deeper into the topic, you can refer to your class textbook or reputable online resources such as Khan Academy or Physics Classroom.

Good luck with your studies, and keep practicing!