D. Free fall
Explanation:
An object is said to be in free fall when there is only one force acting on the body, which is the force of gravity.
Near the Earth's surface, the force of gravity acting on a body is given by
F = mg
where
m is the mass of the body
g is the acceleration of gravity (its value is 
)
The direction of this force is downward (towards the Earth's centre).
If we apply Newton's second law on an object in free-fall, we can find its acceleration. In fact, we have:
And substituting F,
So, every object in free-fall accelerates at towards the ground.
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Acceleration = (change in speed) / (time for the change)
change in speed = (ending speed) - (starting speed)
change in speed = (10 m/s) - (2 m/s) = 8 m/s
Acceleration = (8 m/s) / (4 sec)
Acceleration = (8/4) (m/s²)
<em>Acceleration = 2 m/s²</em>
Answer: 71.7 KJ
Explanation:
The rotational kinetic energy of a rotating body can be written as follows:
Krot = ½ I ω2
Now, any point on the rim of the flywheel, is acted by a centripetal force, according to Newton’s 2nd Law, as follows:
Fc = m. ac
It can be showed that the centripetal acceleration, is related with the angular velocity and the radius, as follows:
ac = ω2 r
We know that this acceleration has a limit value, so , we can take this limit to obtain a maximum value for the angular velocity also.
As the flywheel is a solid disk, the rotational inertia I is just ½ m r2.
Replacing in the expression for the Krot, we have:
Krot= ½ (1/2 mr2.ac/r) = ¼ mr ac = ¼ 67.0 Kg. 1.22 m . 3,510 m/s2 = 71. 7 KJ
Here we apply conservation of linear momentum. The momentum of the truck with cargo and without cargo remains constant. That is,
.
Here 
are initial mass and velocity. 
are final mass and velocity. Here 
and 
.
The velocity of the truck be after its cargo is taken off is
