Answer:
C) the magnitude of the acceleration is a minimum.
Explanation:
As we know that ,the general equation of the simple harmonic motion given as
The displacement x given as
x=X sinω t
Then the velocity v will become
v= X ω cosωt
The acceleration a
a= - X ω² sinω t
The speed of the particle will be maximum when cosωt will become 1 unit.
It means that sinωt will become zero.So acceleration and displacement will be minimum.
Therefore when speed is maximum then acceleration will be minimum.
At the mean position the speed of the particle is maximum that is why kinetic energy also will be maximum and the potential energy will be minimum.
Therefore option C is correct.
The general formula to calculate the work is:

where F is the force, d is the displacement of the couch, and
is the angle between the direction of the force and the displacement. Let's apply this formula to the different parts of the problem.
(a) Work done by you: in this case, the force applied is parallel to the displacement of the couch, so
and
, therefore the work is just equal to the product between the horizontal force you apply to push the couch and the distance the couch has been moved:

(b) work done by the frictional force: the frictional force has opposite direction to the displacement, therefore
and
. Therefore, we must include a negative sign when we calculate the work done by the frictional force:

(c) The work done by gravity is zero. In fact, gravity (which points downwards) is perpendicular to the displacement of the couch (which is horizontal), therefore
and
: this means
.
(d) Work done by the net force:
The net force is the difference between the horizontal force applied by you and the frictional force:

And the net force is in the same direction of the displacement, so
and
and the work done is

Answer:
The minimum coefficient of friction is 0.544
Solution:
As per the question:
Radius of the curve, R = 48 m
Speed of the car, v = 16 m/s
To calculate the minimum coefficient of static friction:
The centrifugal force on the box is in the outward direction and is given by:

where
= coefficient of static friction
The net force on the box is zero, since, the box is stationary and is given by:
This is an elastic collision
bcuz i think they move apart after the collision
sorry if im wrong