Question

Compared to the force needed to start sliding a crate across a rough level floor, the force needed to keep sliding once it is moving is
1) less

2) greater

3) the same

Answer 1

The force to start sliding a crate across a rough level uses the equation:

$F_f = \mu_sN$

The force to keep it moving is given by:

$F_f = \mu_dN$

Notice that N or the Normal Force stays constant because it's the same object throughout the experiment and angle of the ground is also constant. Therefore, only thing that makes a differences are the static and dynamic coefficients of friction. The comparison between them is given by the law:

$\mu_s \geq \mu_d$

Therefore, the force needed to start sliding a crate across a rough level floor is greater than the force needed to keep it sliding once it is moving. So, your answer is 2.

Hope I could help! :)

Answer 2

Answer:

Greater

Explanation:

As we know that when an object is placed on a rough floor then minimum force required to slide the object on the rough surface is known as limiting friction force.

Limiting friction is the maximum value of static friction between the object and ground surface.

So it is given as

$f_s = \mu_sF_n$

Once the object start sliding on the rough surface then the friction force on the object is known as kinetic friction which is given by

$f_k = \mu_kF_n$

now we know that

$\mu_s \geq \mu_k$

So it requires less force to move an object on rough floor once it starts sliding

So the force required to start sliding is greater than the force to move it once it start sliding