Answer:
an example is a bicep curl
Explanation:
A concentric contraction is a type of muscle activation that causes tension on your muscle as it shortens. As your muscle shortens, it generates enough force to move an object.
Answer:
The force does the ceiling exert on the hook is 269.59 N
Explanation:
Applying the second Newton law:
F = m*a
From the attached diagram, the net force in object 1 is:

In object 2:

Adding the two equations:
(eq. 1)
The torque:

Where
I = moment of inertia
α = angular acceleration
If the linear acceleration is

Torque due the tension is equal:

Substituting torque, mass, in equation 1, the expression respect the acceleration is:

Where
W₁ = 75 N
W₂ = 125 N
W = 80 N

The net force is:

The answer is 2. Magnetite. Hope I could help you :)