If you push a box across the floor its "physics work" but if you push on the wall it's not. Which of the following choices best explains why? You're not applying a force to the box but you are applying a force to the wall. The box is moving but the wall is not. The direction of the force on the box is not the same direction as the motion. You're applying a force to the box but you are not applying a force to the wall.

A person drags a sled across a frozen lake to town. The surface of the lake is quite smooth and slippery (so the friction from the ice can be neglected), but he has studded boots with nails driven through the soles (from the inside) so he can walk across the ice without slipping. As he nears his destination, he begins to slow the sled down by pushing in a direction opposite the velocity of the sled. During this process, the work he is doing on the sled is: Positive   Not enough information is given   Negative   Zero

A mechanic pushes a m=2300 kg car from rest. He does W=4850 J of work in the process. During this time the car moves d327 m. Neglect the friction to answer the following questions. What is the horizontal force exerted on the car? Units: What is the velocity of the car at the final distance? Units:

A cord is used to vertically lower an initially stationary block of mass M = 4.9 kg at a constant downward acceleration of g/7. When the block has fallen a distance d = 2.4 m, find (a) the work done by the cord's force on the block, (b) the work done by the gravitational force on the block, (c) the kinetic energy of the block, and (d) the speed of the block. (Note : Take the downward direction positive) (a) Number Units (b) Number Units (c) Number Units (d) Number Units

805 (8 In the figure, a frictionless roller coaster car of mass m =805. kg tops the first hill with speed vo = 18.0 m/s at height h = 41.0m. What is the speed of the car at (a) point A, (b) point B, and (c) point C? (d) How high will the car go on the last hill, which is too high for it to cross? Use g=9.81 m/s?. First hill- h/2 2.

4. Here we prove a version of the work-kinetic energy theorem for an object moving in 1-D subject to a constant force. Consider a mass m, traveling initially at speed v, on which a constant net force F is applied in the same direction as its motion over a distance d. After the net force has acted over this distance, the speed of the object is v2. In terms of m, F, v1, v2, and d only, V, A) What is the acceleration of the mass? t=0 m F d t>0_m B) What is the time over which the mass travels the V, distance d? [Use one equation of constant acceleration to find this.] C) Use another equation of constant acceleration to relate m, F, v,, v2, and d. Show that the product W = Fd is equal to the change in the mass’s kinetic energy.

Common speech often uses the term "work" to refer to situations where, according to the physics definition of work, there is no actual work done. Find an example of this and explain why the non-physics public considers this work and what a proper physics response would be to this error. You must use ordinary language in an attempt to clarify what is happening do not rely on trigonometry or scalar dot products in you answer . Some examples you could consider include a person pushing on a wall and the wall not moving, a person doing a "bench seatisometric exercise where they squat against a wall, the moon being pulled by gravity as it orbits the earth, etc.

(a) Calculate the force needed to bring a 850 kg car to rest from a speed of 90.0 km/h in a distance of 105 m (a fairly typical distance for a nonpanic stop).N(b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exerted on the car and compare it with the force found in part (a), i.e. find the ratio of the force in part(b) to the force in part(a).(force in part (b) / force in part (a))