Newton's 2nd law Definition and 138 Threads

Sorry, but this will be a long post. This isn't homework, I'm reviewing physics after many years of neglect. Halliday & Resnick, 4th Ed., section on variable mass and rockets, refers the interested reader to an article, "Force, Momentum Change, and Motion," Martin S. Tiersten, Am. J...

Homework Statement Attached Homework Equations Attached The Attempt at a Solution 2ac + 3 = 0 => ac = 1.5m/s^2 upwards For FBD of C, Newton's 2nd law 2T - 200g = 200*1.5 => T = 1131N For FBD of the beam, Take moments about A, and assume beam is rigid (CCW positive): 2.5T - 3T -...

I can't derive it properly even though it should be easy: From Newtons 2nd law: m dv/dt = -eE => v(t) = -meEt + v(0) (the latter will average out when taking average) Now the Drude assumption: An electron will on average travel a time τ before being scattered and starting its motion...

I’m supposed to prove that if ΣF(v) = -Av^2, where A is a constant, then Δx = m/A * ln (v0/v) by using Newton’s second law in the form ΣF = m dv/dt. I can solve the problem by using the form ΣF = mv dv/dx; however, it’s specifically stated that I’m not allowed to use the law in that form...

The problem is: In the figure here three ballot boxes are connected by cords, one of which wraps over a pulley having negligible friction on its axle and negligible mass. The masses are mA = 31 kg, mB = 40 kg, and mC = 13 kg. When the assembly is released from rest, (a) what is the tension in...

First of all I'm not sure if this is the right forum for this problem. Homework Statement Given that \overline{F}=m\overline{a} is valid in the lab frame S, show that: (a) it is also valid in a moving frame S' with a constant velocity relative to S, but (b) invalid in a moving frame with...

I haven't taken a physics course in years so I am little lost. A ball is thrown with initial speed $v_0$ up an inclined plane. The plane is inclined at an angle $\phi$ above the horizontal, and the ball's initial velocity is at an angle $\theta$ above the plane. Choose axes with $x$ measured...

1. "A 40.0-kg crate is pulled along a horizontal floor by the ideal arrangement shown in figure below. The force F is 280 N. The coefficient of kinetic friction between the crate and the floor is 0.170. What is the acceleration of the crate?" ______box---^=Pulley__ Okay, this is a...

Homework Statement http://www.diigo.com/item/image/2sb3i/ahcq Homework Equations Ʃ\vec{F} = m\vec{a} The Attempt at a Solution For M : T - mg = ma T - 19.6 = 2a (1) For 2M : 40 cos (150) - T = 4a from (1) : T = 2a + 19.6 substituting : 40 cos (150) - (2a +19.6) = 4a 40 cos (150) - 19.6...

A Person in "Free Fall" Newton's 2nd Law Homework Statement An 80kg aviator is in free fall and acquires a velocity of 60 m/s and then opens his parachute. After falling an additional 30m, his velocity has been reduced to 20 m/s. What is the average acceleration of the aviator while his fall...

If an isolated body starts to accelerate, why would saying the system isn't properly isolated render Newton's second law meaningless? pg. 60 of K&K...

Homework Statement A dockworker applies a constant horizontal force of 80 N to a block of ice on a smooth horizontal floor. The fritional force is negligible. The block starts from rest and moves 11 meter in 5 seconds. What is the mass of the block of ice? Homework Equations Newton's...

Homework Statement We did a lab in class where we had a cart and we had nothing on top of it. We added different forces at the end of a pulley to see how the acceleration differed with different forces. One of the questions on our lab was: We tried to keep the "mass constant". Why is this...

I'm just curious about the second law. I was taught in secondary school that the definition of the 2nd law was just when a resultant force acts on an object with a constant mass, the object will accelerate and move in the direction of the resultant force. The product of the mass and the...

Homework Statement In the figure http://i.imgur.com/Y5Vc7.gif shows a uniform disk (M = 2.5kg, R = 0.20 m) mounted on a fixed horizontal axle. A block (m = 1.2kg) hangs from a massless cord that is wrapped around the rim of the disk. The cord does not slip and there is no friction. Find the...

【Atwood Machine Problem】 Homework Statement Regular atwood machine lab where you test the proportionality of net force and acceleration as stated in Newton's 2nd Law. The regular lab procedure is to release the smaller mass at rest, to let it be lifted by the heavier one. Question is: "How...

Hey guys, how would I show that a = g sin(alpha) for the following diagram?

Homework Statement A lightweight string of length 60.0 cm is attached to the ceiling at points separated by distance D, as shown on the diagram in my attachment. Three objects of equal mass are hung from the string, separating the string into four equal segments of lenth L. If θ=40° , find...

hello all Consider an experiment to prove that the acceleration in a certain direction on a given mass is directly proportional to the resultant force in that direction given that the given mass is constant. The acceleration can be measured using light gates. This resultant force can be...

In Figure 5-51a, a constant horizontal force a is applied to block A, which pushes against block B with a 20.0 N force directed horizontally to the right. In Figure 5-51b, the same force is applied to block B; now block A pushes on block B with a 10.0 N force directed horizontally to the left...

Homework Statement http://rwdacad01.slcc.edu/academics/dept/physics/tvanausdal/2210/problems/force/force3.htm A block is given a push up the incline so it has an initial velocity of 5 m/s up the incline. If the incline angle is 30 degrees and the coefficient of kinetic friction is 0.2...

A body of mass m (kg) is falling vertically under gravity g m/s2 in a medium whose resistance to the speed of the body, v m/s, is proportional to vn (n positive). If the body was released from rest and has terminal velocity, vt m/s, use Newton's 2nd law of motion to show that its...

Hi, I'm having trouble with these problems dealing with Newton's 2nd Law 1] Two blocks are in contact on a frictionless table. A horizontal force is applied to the larger block, as shown in Fig. 5-50. (a) If m1 = 2.0 kg, m2 = 1.4 kg, and F = 2.7 N, find the magnitude of the force between the...

Homework Statement So I am coming up with a word problem dealing with N2L. It goes like this. I have an object on top of a cliff i want to get, so i attach a pulley to the edge of the cliff. Now i tie my self to the object and string it with the pulley. To get the object down I will rappel off...

Homework Statement Homework Equations Newton's 2nd Law F = ma Torque Equation τ = Iα The Attempt at a Solution Well I know I have to write separate equations for the masses and tensions so I got this: T1 - m1g = m1a T2 - m2g = -m2a -----> (negative because acceleration...

A 15,000 kg rocket blasts off from Earth with a uniform upward acceleration of 2.0 m/s2 and feels no air resistance. The thrust force its engines must provide during this acceleration is 30,000 N upward. Apparently this is FALSE! I don't understand why F=MA 30000N=15000kg*2m/s^2...

Homework Statement A proud homeowner is out mowing their lawn. If the force of friction on the mower is 50.0 N and it is accelerating forward at 0.15 m/s2, what is the magnitude of the applied force if the owner is pushing on the handle of the mower at an angle of 70 below the horizontal...

Homework Statement An arrow, starting from rest, leaves the bow with a speed of 25 m/s. If the average force exerted on the arrow would be doubled, all else remains the same, with what speed would the arrow leave the bow? Homework Equations force = mass x acceleration The Attempt at a...

Homework Statement http://gyazo.com/f075da031d0e9d66f269e27628619082.png http://gyazo.com/525919e03d92ae9efad90cc06995ec1b.png Homework Equations F = ma F = 0 The Attempt at a Solution T = Fg for M1 M2 = T - ma = T-M2a I don't know what to do after this.

I understand that force is equal to the time derivative of momentum, or d(mv)/dt. Then what happens if the velocity is constant and only the mass is changing. Does this mean there will be a force. If so, in what direction since I am assuming it is still a vector. Also, what if the mass and...

Homework Statement Block B rests upon a smoot surface. If the coefficients of static and kinetic friction between A and B are mu_s=0.4 and mu_k=0.3, respectively, determine the acceleration of each block if P=6lb. (picture attached below) Homework Equations Using Newton's Second Law...

F = dp/dt = d(mv)/dt = m(dv/dt) + v(dm/dt) = a + v(dm/dt) i don't understand why d(mv)/dt = m(dv/dt) + v(dm/dt) can somone help ? TNX !:smile:

Would the world fall apart and be destroyed if this law ceased to be constant? If not, how can we/do we speculate what would be different? Thanks!

Block inside a spinning cone -- Newton's 2nd Law problem Homework Statement See attempt at solution. I have attached everything there.Homework Equations F_net = m * a_n (net force) W = mg (weight) a_n = 4*pi^2 * R * f^2 ... formula for "normal" component of acceleration where R = radius, f =...

Homework Statement In this problem we explore a slightly more realistic model of a rocket's acceleration still neglecting air resistance. Consider a rocket fired straight up from rest burning fuel at the constant rate of b kg/s. Let v=v(t) be the velocity of the rocket at time t and suppose...

Homework Statement A 5.4 kg mass and a 6.2 kg mass are tied to a light string and hung over a frictionless pulley. What is the tension in the string? Homework Equations F=ma The Attempt at a Solution Not sure how to do this one. I know the tension on the string will be the same at both...

Homework Statement Show that the form of Newton's Second Law is invariant under: (a). a Galilean Transformation (GT) in 1-Dimension. (b). a Galilean Transformation (GT) in 2-Dimensions. (c). a Galilean Transformation (GT) in 3-Dimensions. Homework Equations Newton's Second Law...

If we make a diff. equation from Newtons's 2nd law, and solve it, we will get x(t), where x(t) is the displacement as a function of time. what do the shape of the graph x(t) means? Does it give the trajectory of the motion?

Homework Statement A 1000 kg elevator is held up by two cables. If each able exerts a force of 6000N upwards upon the elevator, find the elevator's acceleration.Homework Equations Fg=mg FNET=maThe Attempt at a Solution I started with a force diagram to help me and then I think I'm supposed...

Hi all, here is a problem that has popped into my head every so often for the last year or so: A small, low-mass body is moving at a constant velocity of 1000m/s through a vaccuum, so it has no acceleration or deceleration i.e. a=0. Now let's say you are an astronaut and you are floating...

Homework Statement A load of 200kg is lifted through 50m by a vertical cable. The load accelerates uniformly from rest for 20 seconds, travels at constant speed for 10 seconds then decelerates to rest in a further 10 seconds. Find the maximum speed attained and the tension in the cable at each...

So i have this general question. When the situation arises in which there are velocity and/or position depended forces acting on an object, would it be generally easier to use the work energy theorem or Newton's 2nd law & kinematics in predicting the motion? My guts tell me it will be work...

Well these two problems were from my quiz, and if I don't find out how to solve them soon, I'm going to spend my whole weekend thinking about them. D8 I'll try to remember the problems as best I can. 1) An astronaut is in space, in the midpoint of two stars that have the same mass. If all...

Mechanics:Dynamics (Newton's 2nd Law?) Homework Statement A sphere S with a mass of 5 kg is attached by a rigid rod to 1 kg block B which is free to slide with no friction in a horizontal slot. The system is released from rest. At the instant when it is released, find the tension in the...

Homework Statement A sphere S with a mass of 5 kg is attached by a rigid rod to 1 kg block B which is free to slide with no friction in a horizontal slot. The system is released from rest. At the instant when it is released, find the tension in the rod and the accelerations of both blocks...

Applying Newton's 2nd law?! Homework Statement A 2.91 kg block starts from rest at the top of a 32◦ incline and slides 1.98 m down the incline in 1.28 s. The acceleration of gravity is 9.8 m/s2 What is the acceleration of the block? Answer in units of m/s2 What is the coefficient...

Homework Statement A man standing in an elevator that is moving with a constant acceleration holds a 3-kg block B between two other blocks in such a way that the motion of B relative to A and C is impending. Knowing that the coefficients of friction between all surfaces are μs = 0.30 and μk =...

Homework Statement There is a box on a platform with mass 3.5kg and it has two ropes connected to it. On the end of each of these ropes are 2 other boxes hanging off the table (so only F_y component). One box is 2.5kg and the other is 1.5kg. I need to find the acceleration of all the boxes...

Homework Statement A chain consisting of five links, each of mass 0.090 kg, is lifted vertically with a constant acceleration of a = 3.6 m/s2. Find the magnitude of the force that link 3 exerts on link 2. Note: The chains are connected vertically Homework Equations \Sigma F = ma The Attempt...

Brand new to the forum. My apologies if this problem is already posted on the site. I searched a bit but had no luck. Homework Statement Problem from Cutnell & Johnson PHYSICS 7th Edition. Chapter 4 - Problem #9 Two forces FA and FB are applied to an object whose mass is 8.0 kg. The...