Answer: 
Explanation:
Given
Mass of child 
speed of child is 
Moment of inertia of merry go round is 
radius 
Conserving the angular momentum

78.4 joules is the energy of a 4 kg apple that is sitting on a 2 m high tree branch.
<u>Explanation:
</u>
When an apple falls to the ground from a tree, its positional energy (stored as potential gravitational energy) turns into kinetic energy, during a fall. Chemical potential energy is chemical energy because it is food and potential energy as it can still have ability to move. So, in the given case, kinetic energy is zero.
To find potential energy, the formula would be

Where, given
m – Mass – 4 kg
(Known value)
h – Height - 2 m
Substitute these values, we get

Similar elements with similar properties were in the same groups and periods for instance lithium(Li) and sodium(Na) are alkaline metals and so belong to the same group (that is group 1).Also Hydrogen(H) and Helium(He) both have only one shell or energy level and so belong to the same period.
Answer: ∆L = 0.49cm ≈ 0.50cm
Therefore there should be 0.5 cm gap between each piece of steel.
Explanation:
Thermal expansion of steel is the increase in size of steel as a result of increased temperature. It can be represented by the mathematical expression:
∆L = L(k)∆T .....1
Where;
∆L is the change in length
L is the initial length
∆T is the change in temperature
k is the specific Linear expansion coefficient.
Given;
L = 12m
∆T = 50°C - 16°C = 34°C
k (for steel) = 1.2 × 10^-6 /C
Substituting the values into the equation 1
∆L = 12 × 34 × 12×10^-6
∆L = 4896 × 10^-6 m
∆L = 0.49cm ≈ 0.50cm
Therefore there should be 0.5 cm gap between each piece of steel.