Question

MODEL ACTIVITY TASKS
CLASS - IX
PHYSICAL SCIENCE
Write the answers to the following questions :
1. Justify or criticize "Although the isobars have same mass numbers their
masses are not exactly same”.
2. Why are the weights in a weight box kept in a 5:2:2:1 ratio?
3. Why is an aeroplane unable to fly in vacuum?
4. From his experiments, how did Rutherford conclude that most of the space
inside an atom is empty?
o
2002
Write the answers to the following questions :​

Answer 1

Answer:

3. because in vaccum no air pressure is present due to which the aeroplane not get the enough pressure to fly

Answer 2

we have to write the answers to the following questions .

solution :

1. Ans : isobars are atoms of different elements that have the same number of nucleons (or mass number). for instance, ⁴⁰K and ⁴⁰Ca are isobars because their nucleons numbers are same.

but carefully read the bold underlined line. those have the same number of nucleons means, (no of protons + no of neutrons) must be same.

but it is obvious that different elements have different atomic no and hence different no of protons.

like, potassium , Z = 19 number of protons = 19 and no of neutrons = 21

while Calcium , Z = 20 no of protons = 20 no of neutrons = 20

also mass of proton < mass of neutron

here it is clear that mass of potassium is definitely not equal to mass of calcium. but their mass numbers are same.

Therefore isobars have same mass numbers but their masses are not exactly.

2. Ans : We still don't know the actual reason behind it. but you can find any number if you have numbers in ratio of 5 : 2 : 2 : 1, try it. i think, The weights in a weight box kept in a 5 : 2 : 2 : 1 ratio because we can weight any form using them.

3. Ans : because the aeroplanes need air for both propulsion and lift. but the vacuum can't provide both of them to the aeroplanes, that's why aeroplanes can't fly in vacuum.

4. Ans : according to Rutherford gold foil experiment, when a ray of alpha particle strikes on the surface of gold foil, most part of the ray penetrates the gold foil and travels in a straight line. it shows that most of the space inside an atom is empty.