Answer:
A. The force exerted by the sprinter must be 9.6 × 10² N.
B. The force that propels the sprinter is exerted by the blocks.
Explanation:
Hi there!
Let´s begin with part B:
The sprinter exerts a force on the blocks and, as a reaction, the blocks exert a force on the sprinter that is of equal magnitude but opposite direction (Newton´s third law). This reaction of the blocks causes the acceleration of the sprinter.
Part A
The force exerted by the blocks can be calculated using Newton´s second law:
F = m · a
Where:
F = exerted force.
m = mass of the object being accelerated.
a = acceleration of the object after applying the force on the object.
F = m · a
F = 64 kg · 15 m/s²
F = 9.6 × 10² N
For this problem the figure below shows the representation of a student who pulls on a 20kg box. We know this variables:
Weight of the box = 20kg
Force used by the student to pull on the box = 50N (This is the tension T)
Angle relative to the horizontal = 45 degrees
Aceleration of the box =
The figure also shows the Free-Body diagram, Applying Newton's Second Law we can find the equation for this diagram, related to the x-axis as:
Isolating
:
<span>That is the friction force on the box.</span>