Question

Q1. Explain the conservation of energy in terms of the energy transformation(s) that occur when you strike (light) a match.

Q2. When you turn on a lamp at home you are using electricity generated by a power company or public utility. Assume the electricity powering the lamp was generated at a coal burning power plant and explain the conservation of energy in terms of the energy transformations that occur when you turn on the lamp.

Q3. Unless you push a pendulum at the start of it's swing (doing work to give it extra energy), will it ever swing higher than it's starting point? Explain your answer in terms of kinetic and potential energy.

Q4. Does a pendulum swing forever? Why or why not?

Q5. Unless you push a pendulum at the start of it's swing (doing work to give it extra energy), will it ever swing higher than it's starting point? Explain your answer in terms of kinetic and potential energy.

Q6. Describe the transformations between potential and kinetic energy when you drop a 15000 gram television from a height of 0.8 meters.

Q7. A car with a mass of 860 kg sits at the top of a 32 meter high hill. Describe the transformations between potential and kinetic energy that occur when the car rolls to the bottom of the hill and continues rolling.

Q8. How is the previous problem different from ones where the object comes to a stop at the end of moving/falling? Discuss what happens to the energy in each case and how they are different.

Q9. Describe the transformations between potential and kinetic energy that occur when a 1000 kg rock falls from the top of a 18 meter cliff.

Q10. How much kinetic energy does a 2000 gram ball have the instant before it hits the ground after falling from a height of 6 meters?

Q11. Assume the collision in problem 10 is perfectly elastic (no energy is lost) and there is no air friction. How high should the ball bounce? Describe the transformations between potential and kinetic energy that will occur from when the ball is dropped till it reaches the top of it's first bounce.

Answer 1

1) when we light a matchstick,the energy which got consumed in while rubbing the matchstick against the surface,turns into heat and hence ,it lights , therefore,the energy gets transferred from one type to another which proves the law of conservation of energy.

2) The coal gets burn and generate into electricity which further used by us for various purposes like lighting lamp and since the energy gets transferred from one source to another instead of ceasing, it proves the statement of conservation of energy.

3) As the pendulum swings in air , it continues to move from one point to another, changing potential energy to kinetic energy due to the motion that's taking place and unless an external force interferes, it's speed won't increase as at some point due to the friction by air will resist the movement resulting in decresement of kinetic energy and increased potential energy, thus ,at some point it will come to rest .

4) No ,it doesn't , because due to the force of friction,the disturbance in the movement of it ,takes place, making it stop at a specific point after some time.

5) As the pendulum swings in air , it continues to move from one point to another, changing potential energy to kinetic energy due to the motion that's taking place and unless an external force interferes, it's speed won't increase as at some point due to the friction by air will resist the movement resulting in decresement of kinetic energy and increased potential energy, thus ,at some point it will eventually come to rest .

6)

• Mass (m)⇢15000 gram = 15 kg
• Height(h)⇢0.8 meters
• Acceleration due to gravity(g)⇢9.8m/s²
• Potential energy ⇢mgh
• Potential energy ⇢(15 x 9.8 x 0.8 )J
• Potential energy ⇢117.6 J

7)

• Mass (m)⇢15000 gram = 860 kg
• Height(h)⇢32meters
• Acceleration due to gravity(g)⇢9.8m/s²
• kinetic energy ⇢mgh
• kinetic energy ⇢(860 x 9.8 x 32 )J
• kinetic energy ⇢269,696 J

8) In the previous problem ,the kinetic energy increases as continues rolling and the potential energy decreases in this process of prolongation of the movement ,while ,when an object comes to rest after the process of moving or falling, it's potential energy is at the highest while the kinetic energy is just the opposite .

9)

• Mass (m)⇢ 1000kg
• Height(h)⇢18 meters
• Acceleration due to gravity(g)⇢9.8m/s²
• Kinetic energy ⇢mgh
• Kinetic energy ⇢(1000x 9.8 x 18 )J
• Kinetic energy ⇢176,400 J

10)

• Mass (m)⇢ 2000 gm = 2kg
• Height(h)⇢6meters
• Acceleration due to gravity(g)⇢9.8m/s²
• Kinetic energy ⇢mgh
• Kinetic energy ⇢(2x 9.8 x 6 )J
• Kinetic energy ⇢117.6 J

11)

In perfectly elastic collision, there's no loss of energy, hence ,the energy that got used up in the starting to bounce the ball ,will remain the same throughout the whole collision and the height would be the same 6 meters and kinteic energy would be 117.6J