Advertisements
Advertisements
प्रश्न
If the energy of a ball falling from a height of 10 metres is reduced by 40%, how high will it rebound?
Advertisements
उत्तर
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
संबंधित प्रश्न
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.
In an electric fan, electrical energy changes into the mechanical energy.
Write true or false of the following statement.
One form of energy cannot be converted into another form.
Fill in the blank
The S.I.unit of energy is ______
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 |
Tick the most appropriate answer.
The force applied on a machine to do work is called the
Answer the following in short.
What do you understand by the term efficiency of a machine’?
Define the term 'watt'.
What is the common name of '1 kWh' of electrical energy?
A cell converts one form of energy into another form. Name the two forms.
- 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.
The capacity that an object has for doing work is called ______.
Can you tell?
When can we say that displacement has taken place?
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.
 |
 |
 |
 |
 |
 |
Which one of the following is not the unit of 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)
