I can confirm it is not b.
If there's a friction force of 20N toward the left, then you need to apply
a force of 20N toward the right, in order to keep the box moving at a
constant speed.
When there's a force pointing to the left and an equal force pointing
to the right, then the forces on the box are "balanced" ... they add up
to zero, and the box has zero acceleration. That means it moves in a
straight line at a constant speed.
Explanation:
Given:
The cross product is given by
Here we will say that there is no external torque on the system so we will have
here we know that
where we know that
Also we know that
initial angular speed will be
now from above equation
now we have
so final speed will be 2.41 rad/s
To solve this problem we will apply the concepts related to the Force of gravity given by Newton's second law (which defines the weight of an object) and at the same time we will apply the Hooke relation that talks about the strength of a body in a system with spring.
The extension of the spring due to the weight of the object on Earth is 0.3m, then
The extension of the spring due to the weight of the object on Moon is a value of , then
Recall that gravity on the moon is a sixth of Earth's gravity.
We have that the displacement at the earth was , then
Therefore the displacement of the mass on the spring on Moon is 0.05m