Answer:
Let the mass of the book be "m", acceleration due to gravity be "g", velocity be "v" and height be "h".
Now if we are holding a book at a certain height (h), <em><u>the potential energy will be maximum which is equal to mass× acceleration due to gravity× height (= mgh)</u>.</em>
(Remember: kinetic energy =0)
Now we consider that the book is dropped, in this case a force will act downward towards the centre of the earth, <em><u>Force= mass× acceleration due to gravity (F=mg)</u></em>. It is equal to the weight of the book.
While the book is falling, the potential energy stored in the book converts into kinetic energy and strikes the floor with <em><u>the maximum kinetic energy= (1/2)×mass×velocity² (=1/2mv²)</u>.</em>
(Remember: kinetic energy=0)
Due to this process the whole energy is conserved.
As the potential energy decreases kinetic energy increases.
Index fossils are used to determine the relative ages of rock and fossils and are also used to define the boundaries between geologic periods.
<u>Option: A</u>
<u>Explanation:</u>
The fossils which are recognized as fossils guides or indicator fossils are used to classify and recognize geological or faunal periods, termed as index fossils. It must be of short vertical reach, wide geographic distribution and swift patterns in evolution. It helps to assess the rock layers ' age and helps to date other fossils found close and around them. For an instance, Ammonites were abundant in the Mesozoic period between 245 to 65 mya, they have not been found after the Cretaceous era, as they became endangered during the K-T extinction (65 mya).
Answer:
Option (C)
Explanation:
The nuclear energy is defined as a type of energy which liberates either by the process of nuclear fusion or nuclear fission and is mainly used to generate electricity. This energy is stored in the core of an atom (or nucleus).
It is highly effective, cost-effective and there is no emission of greenhouse gases.
But it also has some disadvantages, of which one is that it produces radioactive waste materials, which are difficult to dispose these substances and is also a very expensive method. These materials emit radiations that are harmful to the organisms. So, it is very challenging to dispose these radioactive waste materials.
Thus, the correct answer is option (C).
Answer
given,
initial speed of hockey player= 0 m/s
mass of the helmet, m = 1.3 Kg
initial speed of the helmet, u = 0 m/s
final speed of the helmet, v = 6 m/s
recoil speed of the hockey player, v' = 0.25 m/s
we need to calculate the mass of the hockey player, M = ?
using conservation of momentum
m u + M u' = M v' + m v
initial speed of ice skater is zero
1.3 x 0 + M x 0 = M x (-0.25) + 1.3 x 6
negative sign is taken because recoil velocity is in opposite direction
0 = -0.25 M + 7.8
0.25 M = 7.8
M = 31.2 Kg
Hence, the mass of the young hockey player is equal to 31.2 Kg
