Answer:
Dynamic flexibility
Explanation:
Dynamic flexibility can be generally defined as the ability of the body muscles and joints to move in full range of motion. High flexibility in these joints and muscles leads to the decreasing pain and injury in different parts of the body.
Proper warm up exercises are needed to be carried out that involves both the combination of controlling movements and stretching of the body, and this directly enhances the dynamic flexibility of the body.
The athletes and sports persons possesses a good dynamic flexibility of their body as they carry our different types of body exercises.
The magnitude of the force of friction is 40 N
Explanation:
To solve the problem, we just have to analyze the forces acting on the student and the scooter along the horizontal direction. We have:
- The constant pushing force forward, of magnitude F = 40 N
- The frictional force, acting backward, 
Since the two forces are in opposite direction, the equation of motion is

where
m is the mass of the student+scooter
a is the acceleration
However, here the scooter is moving at constant speed: this means that its acceleration is zero, so
a = 0
And therefore,

which means that the magnitude of the force of friction is also equal to 40 N.
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Answer:
F = - k (x-xo) a graph of the weight or applied force against the elongation obtaining a line already proves Hooke's law.
Explanation:
The student wants to prove hooke's law which has the form
F = - k (x-xo)
To do this we hang the spring in a vertical position and mark the equilibrium position on a tape measure, to simplify the calculations we can make this point zero by placing our reference system in this position.
Now for a series of known masses let's get them one by one and measure the spring elongation, building a table of weight vs elongation,
we must be careful when hanging the weights so as not to create oscillations in the spring
we look for the mass of each weight
W = mg
m = W / g
and we write them in a new column, we make a graph of the weight or applied force against the elongation and it should give a straight line; the slope of this line is sought, which is the spring constant.
The fact of obtaining a line already proves Hooke's law.