Question

Give one example of each of the following: (i) Small mass but high kinetic energy (ii) Large mass but low kinetic energy (b) Prove mathematically that the total mechanical energy of a freely falling body in air is conserved.

  • Work and energy CBSE Class 9
WhatsApp

Answer

(a) (i) A cricket/hockey ball which has been hit hard and is travelling fast.

(ii) A shot put thrown by an athlete

(b) Let the body of mass m at height h above the ground starting from rest, be falling freely.

Total energy of the body at height h

= mgh (PE) + 0 (KE) = mgh

After the body has fallen freely through a distance x (say),

KE = mgh, PE = mg (h โ€“ x)

Total energy = KE + PE

= mgh + mg (h โ€“ x) = mgh

When it reaches the ground KE ={1\over2} m.2gh = mgh

PE = 0, Total Energy = KE + PE = mgh

Thus, the total mechanical energy, which is the sum of KE and PE is always equal to mgh.

Was this answer helpful?

Didn't liked the above answer ?

Text Generation Tool

๐Ÿ’ก Some Related Questions

Work power and energy

Shyam and his friends were playing with a catapult (gulel) in his garden. Several mangoes were dislodged and fell with the help of catapult. One of his friend was aiming the catapult on a bird. Shyam prevented him from doing so. (๐’Š) Name the energy possessed by the stretched string of the catapult. (๐’Š๐’Š) What will happen if the stone is thrown without stretching the string of a catapult? (๐’Š๐’Š๐’Š) Why did Shyam prevent his friend from aiming at the bird? Which quality is highlighted in Shyam’s behavior?

Open Answer ยป
Work power and energy

Prachi and Kanchi were observing a building having two different staircase. One slanting and other vertically spiral. Prachi was of the opinion that a person using slanting staircase will be doing more work against gravity but Kanchi thought otherwise. They started arguing. Sanchi, their friend, explained and gave entirely different view and pacified them. (๐’Š) What according to you was the explanation given by Sanchi? (๐’Š๐’Š) What appreciable values do you see in Sanchi?

Open Answer ยป
Work power and energy

Ram’s family was worried about heavy electricity bills to be paid. Their neighbour Mohan suggested some easy and effective steps to reduce the same. Next month’s bill came as a relief to Ram, as the consumption of electricity had reduced by 50 units and so had the bill. (๐’Š) In what other aspects of life can this situation help? (๐’Š๐’Š) What is the unit of energy? (๐’Š๐’Š๐’Š) Write any three steps that you think Mohan might have suggested to Ram.

Open Answer ยป
Work power and energy

On a railway station, a passenger hires a coolie to pick his luggage and carry it to the train. When the coolie finished his work, he asked for the money. But the passenger refused to pay him saying that he has done no work. Answer the following questions based on the above information: (๐’Š) Was the passenger right in saying so? (๐’Š๐’Š) What values are not promoted by the passenger? (๐’Š๐’Š๐’Š) Give a situation seen in everyday life when no work is said to be done by you even though you get tired.

Open Answer ยป
Work power and energy

Figure shows a conveyor belt transporting a package to a raised platform. The belt is driven by a motor. (๐’Š) State three types of energy, other than gravitational potential energy, into which the electrical energy supplied to the motor is converted. (๐’Š๐’Š) The mass of the package is 36 kg. Calculate the increase in the gravitational potential energy (P.E.) of the package when it is raised through a vertical height of 2.4 m. (๐’Š๐’Š๐’Š) The package is raised through the vertical height of 2.4 m in 4.4 s. Calculate the power needed to raise the package. (๐’Š๐’—) Assume that the power available to raise package is constant. A package of mass greater than 36 kg is raised through the same height. Suggest and explain the effect of this increase in mass on the operation of the belt.

Open Answer ยป