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Hi there.
00:01
So for this problem, we have an object that is being held against a wall initially at rest.
00:08
So we know that the speed is equal to zero.
00:12
And the coefficient of friction is equal to 0 .6.
00:17
And the object has a mass m that is equal to 2 kilograms as is shown in the figure.
00:25
And you are holding it with a force.
00:29
You're applying a force that is equal to 30 newtons.
00:36
So the question in here is how long will it the object take to slide down a distance delta y, that in this case because it is moving down where we're going to set that that distance is negative and that is minus one meter.
00:55
So the first thing that we need to find is the acceleration.
01:00
And with the acceleration, we can use kinematics in order to obtain the time that it takes to reach one meter with that acceleration.
01:11
Now, in this case, the acceleration is going to be less than the acceleration due to gravity because we are applying some force in the x direction.
01:22
So what we are going to do first is to assume all of the forces that are acting on the y component.
01:29
And first i'm going to draw the forces in here.
01:33
So there is going to be the weight of the block, which is the mass times acceleration due to gravity, and a frictional force that prevents this from moving.
01:44
Now, and those are the only two forces that are acting on the wide direction.
01:51
So we're going to have the frictional force minus the weight is equal to the mass times the acceleration, because as the problem states, the block is going to move, so it is going to have some acceleration.
02:07
Now, in here, we can solve for the acceleration, so we're going to have that that is the frictional force divided by the mass minus the acceleration due to gravity.
02:19
Now, from the sum of the forces in the x component, we are going to have two forces.
02:26
Those are the force that is being applied, and the other force is the normal force that is always perpendicular to the surface of compton.
02:37
In this case, the surface of compton is the wall, so it's going to be in this direction.
02:43
So we're going to have in here the normal force minus 30 newtoms is equal to zero because the block is not going to move in the x direction, so it's going to have a zero acceleration in that direction...