course PHY 121 This assignment did not show up in my send file so I copied it from the master file. The date is the 6/16 ???Vw???????sStudent Name:
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21:20:55 `questionNumber 100000 `q001. If a block of mass 10 kg accelerates at 2 m/s^2, then what net force is acting on the block?
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RESPONSE --> 20 joules?
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21:21:19 `questionNumber 100000 The net force on the block is the product F = m * a of its 10 kg mass and its 2 m/s^2 acceleration. The net force is therefore F = 10 kg * 2 m/s^2 = 20 kg * m / s^2. The unit of force, which is the product of a quantity in kg and another quantity in m/s^2, is just the algebraic product kg * m/s^2 of these two units. This unit, the kg * m / s^2, is called a Newton. So the net force is 20 Newtons.
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RESPONSE --> ok I missed the Newtons part...
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21:22:29 `questionNumber 100000 `q002. How much force must be exerted by someone pulling on it to accelerate a 10 kg object at 2 m/s^2?
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RESPONSE --> 20 Newtons?
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21:22:38 `questionNumber 100000 This depends on what forces might be resisting the acceleration of the object. If the object is accelerating on a surface of some type, then there is a good chance that a frictional force is opposing the motion. If the object is being pulled upward against the force of gravity, then more force is required then if it is sliding along a low-friction horizontal surface. If it is being pulled downhill, the force exerted by gravity has a component in the direction of motion and perhaps even less force is required. However, in every case the net force, which is the sum of all the forces acting on the object, must be 20 Newtons. The person pulling on the object must exert exactly enough force that the net force will be 20 Newtons.
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RESPONSE --> ok
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21:29:05 `questionNumber 100000 `q003. If friction exerts a force of 10 Newtons in the direction opposite the motion of a 10 kg object, then how much force must be exerted by someone pulling on it to accelerate the 10 kg object at 2 m/s^2, with the acceleration in the same direction as the motion?
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RESPONSE --> I need to see an exaple that I can understand... 10 = 20 kgm/s^2 I don't know yet...I am just trying to figure it out.
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21:32:27 `questionNumber 100000 Since the 10 Newton frictional force is in the direction opposite to motion, and since the acceleration is in the same direction as the motion, the frictional force is opposed to the accelerating force. If the direction of motion is taken as positive, then the frictional force will be in the negative direction and can be denoted fFrict = - 10 Newtons. To achieve the given acceleration the net force on the object must be net force = 10 kg * (+2 m/s^2) = +20 kg * m/s^2 = +20 Newtons. In order to achieve the +20 Newton net force when there is already a frictional force of -10 Newtons, it should be clear that a force of +30 Newtons is required. This can be thought of as 10 Newtons to overcome friction and another 20 Newtons to achieve the required net force.
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RESPONSE --> I am sort of understanding this
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21:38:01 `questionNumber 100000 `q004. How can we write an equation to solve this problem? Hint: What equation would relate the net force Fnet, the force F exerted by the person and the force fFrict of friction?
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RESPONSE --> f = de/ds???
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21:40:26 `questionNumber 100000 If Fnet is the net force and F the force actually exerted by the person, then Fnet = F + fFrict. That is, the net force is the sum of the force exerted by the person and the frictional force. We know that Fnet is +20 Newtons and fFrict is -10 Newtons, so we have the equation 20 Newtons = F + (-10 Newtons). Solving for F we see that F = 20 Newtons + 10 Newtons = 30 Newtons.
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RESPONSE --> I sort of understand but where how does the -10 newtons become positive
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21:44:51 `questionNumber 100000 `q005. If a constant net force of 12 Newtons acts on a cart of mass 6 kg, then at what rate does the velocity of the cart change?
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RESPONSE --> Is it 72 joules??I don't understand how to do velocity with this.... I would say 12/6 and get 2 of something?
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21:45:40 `questionNumber 100000 The velocity of the cart will change at a rate a which is related to the net force and the mass by Fnet = m * a. Thus a = Fnet / m = 12 Newtons / (6 kg) = 12 kg * m/s^2 / (6 kg) = 2 m/s^2. We note that the force unit Newtons is broken down to its fundamental units of kg * m / s^2 in order to perform the unit calculation. Dividing kg * m / s^2 by kg we have (kg / kg) * m/s^2 = m/s^2. It is important to always do the unit calculations. This habit avoids a large number of errors and also can be used to reinforce our understanding of the relationships in a problem or situation.
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RESPONSE --> Okay so all I needed to do was find velocity like I have been...I didn't realize that it was them/s^2 but I get that now
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21:49:55 `questionNumber 100000 `q006. If a force of 50 Newtons is exerted in the direction of the object's motion by a person, on a 20 kg object, and if friction exerts a force of 10 Newtons opposed to the direction of motion, then what will be the acceleration of the object?
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RESPONSE --> 50/20 =I know I have 2.5 kg/s^2 I don't know what to do here yet either I can't undersatnd the book and the quantities and relationships page doesn't help yet since I do not know the fundamentals
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21:52:24 `questionNumber 100000 The object will accelerate at a rate determined by Newton's Second Law, Fnet = m * a. The acceleration will therefore be a = Fnet / m. The net force on the object will be the sum of the 50 Newton force in the direction of motion and the 10 Newton force opposed to the direction of motion. If we take the direction of motion as positive, then the net force is Fnet = 50 N - 10 N = 40 N. It follows that the acceleration is a = Fnet / m = 40 N / (20 kg) = 40 kg m/s^2 / (20 kg) = 2 m/s^2.
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RESPONSE --> Ok Isee that ...I have to first get used to finding Fnet so if the forse is opposed to the direction I subtract and otherwise I add?
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21:57:30 `questionNumber 100000 `q007. If a force of 50 Newtons is exerted opposite to the direction of the object's motion by a person, on a 20 kg object, and if friction exerts a force of 10 Newtons opposed to the direction of motion, then what will be the acceleration of the object?
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RESPONSE --> Fnet =-50 - 10 =-60 a= -60/20kg = -3m/s^2 I don't know if you can even have a negative but I still don't undersatnd how you decide to add or subtract
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21:58:58 `questionNumber 100000 If we take the direction of motion to be positive, then since both the 50 Newton force and the 10 Newton force are opposed to the direction of motion the net force must be net force = -50 Newtons - 10 Newtons = -60 Newtons. The acceleration of the object will therefore be a = Fnet / m = -60 Newtons / (10 kg) = -60 kg * m/s^2 / (20 kg) = -3 m/s^2. The fact that the acceleration is opposed to the direction of motion indicates that the object will be slowing down. The force exerted by the person, being in the direction opposite to that of the motion, is seen to be a retarding force, as is friction. So in this case the person is aided by friction in her apparent goal of stopping or at least slowing the object.
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RESPONSE --> oh my...I did it right...yah although I dont understand this step= -60 Newtons / (10 kg)
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22:01:15 `questionNumber 100000 `q008. If a 40 kg object is moving at 20 m/s, then how long will a take a net force of 20 Newtons directed opposite to the motion of the object to bring the object to rest?
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RESPONSE --> -20/40 =-.5 I don't know yet
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22:06:54 `questionNumber 100000 The force on the object is in the direction opposite its motion, so if the direction of motion is taken to be positive the force is in the negative direction. We therefore write the net force as Fnet = -20 Newtons. The acceleration of the object is therefore a = Fnet / m = -20 Newtons / 40 kg = -20 kg * m/s^2 / (40 kg) = -.5 m/s^2. We can therefore describe uniformly accelerated motion of the object as v0 = 20 m/s, vf = 0 (the object comes to rest, which means its velocity ends up at 0), a = -.5 m/s^2. We can then reason out the time required from the -20 m/s change in velocity and the -.5 m/s^2 acceleration, obtaining `dt = 40 seconds. We can confirm this using the equation vf = v0 + a `dt: Solving for `dt we obtain `dt = (vf - v0) / a = (0 m/s - 20 m/s) / (-.5 m/s^2) = -20 m/s / (-.5 m/s^2) = 40 m/s * s^2 / m = 40 s.
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RESPONSE --> ok I got the first step right but didn't know where to go from there ok I see that I use the same as I have been for dt ...I think I get this if I can see the formula...
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22:10:08 `questionNumber 100000 `q009. If we wish to bring an object with mass 50 kg from velocity 10 m/s to velocity 40 m/s in 5 seconds, what constant net force would be required?
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RESPONSE --> 10m/s - 40m/s = -30m/s /50kg =-.6 m/s I don't know..I
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22:11:58 `questionNumber 100000 The net force would be Fnet = m * a. The acceleration of the object would be the rate which its velocity changes. From 10 m/s to 40 m/s the change in velocity is +30 m/s; to accomplish this in 5 seconds requires average acceleration 30 m/s / (5 s) = 6 m/s^2. Thus the net force required is Fnet = 50 kg * 6 m/s^2 = 300 kg m/s^2 = 300 Newtons.
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RESPONSE --> ok I was headed in the right direction sort of I just have trouble organizing what foes where...I know that for this problem all I need is accelration and then just plug it in
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22:18:25 `questionNumber 100000 `q010. If a constant net force of 50 Newtons brings an object to rest in four seconds from an initial velocity of 8 meters/second, then what must be the mass of the object?
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RESPONSE --> f = m*a so... 4 s - 8m/s = -4 m/s 4-m/s / 50 Newtons???? I am unsure what to do.
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22:20:25 `questionNumber 100000 We know the net force and we have the information required to calculate the acceleration. We will therefore be able to find the mass using Newton's Second Law Fnet = m * a. We first find the acceleration. The change in velocity from 8 m/s to rest is -8 m/s, and this occurs in 4 seconds. The acceleration is therefore -8 m/s / (4 s) = -2 m/s^2. The 50 Newton net force must be in the same direction as the acceleration, so we have Fnet = -50 Newtons. We obtain the mass by solving Newton's Second Law for m: m = Fnet / a = -50 N / (-2 m/s^2) "