A. a child gently swinging on a swing at small angles all the time
Answer:

Explanation:
Given that
J(r) = Br
We know that area of small element
dA = 2 π dr
I = J A
dI = J dA
Now by putting the values
dI = B r . 2 π dr
dI= 2π Br² dr
Now by integrating above equation


Given that
B= 2.35 x 10⁵ A/m³
r₁ = 2 mm
r₂ = 2+ 0.0115 mm
r₂ = 2.0115 mm

By putting the values


I'm really not sure if this is right but I'll try.
The distance that the dog traveled is probably all of the distances added up. I would guess that it's 67 meters in total.
The displacement is a little more tricky but you pretty much have to put a mental map in your head. Since East and West are both 8 meters, they cancel each other out. He travels more southern and that means the displacement is 9 meters south of his original location
Answer:
This is because below 4°c, water unlike other materials becomes less dense when it's temperature is further lowered.
Explanation:
Due to the unusual nature of water; at about 4°c, the behavior of the density of water in relation to its temperature reverses. This means that water becomes less dense as it becomes colder below 4°c. The colder parts therefore floats to the top of the water body while the warmer part sinks allowing the top to freeze and the remaining body below to remain in its liquid state.
The freezing of the top of the lake alone protects the remaining depth of water from freezing by acting as an insulator and preventing further heat loss from the water to the ambient space. If this had not been the case, and water froze all through, marine lives will freeze to death and it will be more difficult to melt the ice come the next summer.
This behavior is due to the hydrogen bonding of the water molecules.
Explanation:
It is given that,
Mass of the crate, m = 50 kg
Force acting on the crate, F = 10 N
Angle with horizontal, 
Let N is the normal force acting on the crate. Using the free body diagram of the crate. It is clear that,


N = 486.57 N
or
N = 487 N
If a is the acceleration of the crate. The horizontal component of force is balanced by the applied forces as :




or

So, the normal force the crate and the magnitude of the acceleration of the crate is 487 N and
respectively.