Advertisements
Advertisements
Question
If the energy of a ball falling from a height of 10 metres is reduced by 40%, how high will it rebound?
Advertisements
Solution
Given:
Height (h1) = 10 m
PE2 = PE1 - PE1 of 40%
Find: Height (h2)
Formula: P.E. = mgh
Calculations:
PE1 = mgh1 ...(i)
PE2 = mgh2 ...(ii)
PE2 = PE1 of 60%
Dividing equation (ii) by (i).
`"PE"_2/"PE"_1 = ("mgh"_2)/("mgh"_1)`
`(60%"PE"_1)/("PE"_1) = "h"_2/10`
`60/100 = "h"_2/10`
`"h"_2 = (60 xx 10)/100`
h2 = 6 m
∴ The ball will bounce up to a height of 6 m when it hits the ground.
APPEARS IN
RELATED QUESTIONS
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Write true or false of the following statement.
In an electric fan, electrical energy changes into the mechanical energy.
Write true or false of the following statement.
Potential energy changes into kinetic energy when it is put to use
Fill in the blank
An electric fan converts electrical energy into ______ energy.
Fill in the blank
The S.I.unit of energy is ______
Select the correct alternatives
The correct statement is
What is potential energy ? State its unit.
State two factors on which the potential energy of a body at a certain height above the ground depends.
Answer the following in a word or two or in a sentence.
Write the formula for calculating the efficiency of a machine.
Derive the relation between commercial unit of energy (kWh) and SI unit of energy (joule).
The commercial unit of energy is :
- Take two aluminium channels of different lengths.
- Place the lower ends of the channels on the floor and hold their upper ends at the same height.
- Now take two balls of the same size and weight and release them from the top end of the channels. They will roll down and cover the same distance.
- At the moment of releasing the balls, which energy do the balls have?
- As the balls roll down which energy is converted into which other form of energy?
- Why do the balls cover the same distance on rolling down?
Note: The question is wrong. It should be "Why do the balls cover the same distance after rolling down"? - What is the form of the eventual total energy of the balls?
- Which law related to energy does the above activity demonstrate? Explain.
Can you tell?
When can we say that displacement has taken place?
Can you tell?
What should be taken into account for measuring work?
We make useful objects from a variety of substances. Another use of substances is that we get energy from some of them.
When we have run a long distance, we feel tired. We have to stop. Why is that?
What energy transfer happen in a car engine?
When a body falls freely towards the earth, then its total energy
The weight of a person on planet A is about half that on the earth. He can jump up to 0.4 m in height on the surface of the earth. How high he can jump on planet A?
A ball is dropped from a height of 10 m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back? (g = 10 m s–2)
