In order for work to be done(A)a machine must be used(B)force must be exerted through a distance(C)a distance must be traveled without the exertion of a force(D)no potential energy may be changed to kinetic energy.
128917
I was a physics student...it's B.
459691
The braking force was enough to dissipate the kinetic energy.\n\nForce x distance = work = kinetic energy\n\nma x 160 = mv^2/2 , notice that m cancels out\n\n160a = v^2/2, solve for v...
536645
This is an energy balance situation.  The work done in dragging the object must equal the energy change.  In this case the energy is potential energy, given by m*g*∆h, where ∆h is the change in vertical distance.  The work (energy) required to drag the block is force times distance along the incline.  Equate these two quantities and solve for F.
128435
B.  The acceleration is towards the Earth and the force is constant.
367681
(a) Work done by gravity = change in potential energy of the book. Now change in potential energy = m*g*h2 - m*g*h1=2*10*(10-1.5) =  170J. So, work done by gravity is 170J\n(b)Change in gravitational potential energy = work done = 170J as explained above.\n(c) Potential energy when textbook is released = m*g*h1 = 2*10*10=200J\n(d) Potential energy when it reaches the hands = m*g*h2 = 2*10*1.5=30J\n(e) If U =100J at ground level, work done by gravity = 170J, the work done does not change with change in reference.\n(f) change in potential energy also remains 170J\n(g) U at release point = 100 + 2*10*10 = 300J\n(h) U at hands = 100 + 2*10*1.5 = 130J
671688
A machine is simply an object that does work. A machine transforms electrical energy into mechanical energy (simple machines excluded).\n\nWhen you think of "work" being done you usually think of some sort of movement occurring.\n\nAn oven is not a machine in that no "work" is being done. An oven just takes electrical energy & transforms it into heat energy.
102564
Work equals the vectors of energy.
222354
None. It takes no power to maintain that speed (on level ground, no friction). The object has kinetic energy (0.5 * m * v^2). Power was required to put it in motion and power can be recovered by decelerating it. If you do the math, the energy is 3551.86 ft-lb, equivalent to 1 horsepower for 6.458 seconds. Answer 1 neglected the fact that weight must be converted to mass by dividing by g, and energy is proportional to v^2.
466450
You've missed a unit, but I'm going to assume the distance is 5.6 metres ...\n\n(Velocity) = (Work) = (Force) * (Distance)\n\n and\n\n(Force) = (mass) * (acceleration)\n\ntherefore \n\n(Force) = (mass) * (distance) / (velocity)\n\n... plugging in the numbers, we get   57.8 kg.m/s/s ... = 57.8 N.
364708
1. friction\n2. W=mg  , he has a mass of 100Kg. Weight is the force=newtons, g=pull of gravity N=100 x 9.8m/sec^\n98Newtons\n3. correct
530304
Work is force times distance.  Since he is not moving the mass, he is doing no work.  \n\nHowever, his body has used a lot of energy and his muscles are tired.  This is because your body needs energy to stay upright and balanced.  It needs even more energy if you are balancing a load.  Unfortunately, all that energy has been converted to heat, and not towards doing any work.  What a waste.
572706
Power = work done per unit of time.\n\nP=W/T
641214
work = change of kinetic enegy\nW = 1/2 m (vf² - vi²)\nW = 0.5 * (0.250 kg) * (16² - 20²) m²/s²\nW = -18 J
132613
well, using f=ma, and w=fd, we immediately get w=(ma)d\nW=work  (3650 joules)\nM=mass  257kg\na=accelleration =gravity =9.81\nd=distance (required)\n\nrearrange w=(ma)d\n\nd=w/(ma)\nDistance=work/(mass*acceleration)\n\n= 3650/(253*9.81)\n=1.47m
446702
(a) Gravity exerts a downward force on the block of 9.8 Newtons/kg * (0.25 kg) = 2.45 Newtons. Work done by gravity = force * distance = 2.45 Newtons * 0.12 m = 0.294 Joules\n\n(b) The spring is a bit tougher since the upward force increases as the spring is compressed. Force = 250 N * (C) where C is the distance the spring has been compressed (in meters). Work is then the integral of Force over distance, so Int(250 * C (dC)) from C = 0 to 0.12 M . The integral is 125 * C^2. Evaluation at 0 gives 0. Evaluation at 0.12 gives 125 (0.12)^2 =  1.8 Joules. So the work done by the spring is -1.8 Joules . Note that the work is negative, because the object is moving against the applied force.\n\n(c) When the block strikes the spring, it will have a kinetic energy of (1/2)mv^2 = (1/2)(0.25kg)v^2 = 0.125v^2.\nThis kinetic energy is absorbed by the spring as it compresses. Note that the work done by gravity is also absorbed by the spring.\nTherefore, we have the following equation:\n0.125v^2 + 0.294 = 1.8\nv^2 = 8(1.8-0.294) = 8(1.506) = 12.048\nSpeed of block just before it hits = SQRT(12.048) = 3.47 meters/sec downward.\n\n(d) I'll leave this as an exercise for you. Just apply the same techniques as above. Note that the block hits the spring with a velocity of 2(3.47) = 6.94 meters per second...
13742
Assuming it can't be II and III, I would say it's all of the above. The potential energy is converted into kinetic - the velocity increases and the height decreases. The KE + PE remains constant, because there is no work being done because there is no force here (besides gravity). However, the first depends on how you define mechanical energy - if it's kinetic energy, it's true. If not, I really don't know what it is.
429058
Work is commonly defined as the dot product of force and displacement.  Essentially this means that you are moving in the same or exact opposite direction as your field lines for your given force.  Example: Friction does work to stop a moving box as the force is directed anti-paralell to your direction of travel.\n\nWhen you move in a circle, centripetal force is always directed toward the inside of the circle, which is exactly perpendicular to your direction of motion in the circle.  Since the force is perpendicular to the direction of motion, there is no work done.