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
Write true or false of the following statement.
A gum bottle lying on a table has no 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
Cooking gas converts _______ energy into heat energy.
Fill in the blank
The ability to do work is called ______
Match the following columns
| COLUMN A | COLUMN B |
| 1. Running water | 1. heat energy |
| 2. Burning | 2. vibrations |
| 3.Energy | 3.atom bomb |
| 4.Sound energy | 4.kinetic energy |
| 5.Nuclear energy | 5.joule |
State the unit of energy and define it.
What do you mean by conservation of mechanical energy? State the condition when does it hold.
Match the following:
| Column A | Column B |
| (a) Needle | (1) class II lever |
| (b) Doorknob | (2) inclined plane |
| (c) Ramp | (3) Class I lever |
| (d) Lemon crusher | (4) Wheel and axle |
| (e) Seesaw | (5) wedge |
Define the term efficiency of a machine.
Answer the following in a word or two or in a sentence.
Write the formula for calculating the efficiency of a machine.
Give a reason for the following.
The efficiency of a machine is always less than 100%.
Define the term 'watt'.
A certain household consumes 650 units of electricity in a month. How much is this electricity in joules?
The commercial unit of energy is :
Can you tell?
What should be taken into account for measuring work?
Observe the picture and put a tick (✓) if work is done and put a cross (x) if work is not done.
 |
 |
 |
 |
 |
 |
Find out the form of energy possessed by the following thing.
A rock on the top of a hill
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?
