1	Kinetic Energy and Work
2	Energy Types of Energy?
3	Work Work is energy transferred to or from an object by means of a force acting on the object. Energy transferred to the object is positive work, and energy transferred from the object is negative work.
4	Work and Kinetic Energy
5	Work- Kinetic Energy Theorem K_f – K_i = Δ K = W
6
7	"In the figure" In the figure: Two men slide an initially stationary safe of mass m=225 kg on a frictionless floor. F₁ =12.0 N and F₂ = 10.0 N What is the net work done on the safe by F₁ and F₂ during the displacement d. during the displacement d, what is the work done by the weight of the safe and the normal force? What is the final speed of the safe if d= 8.50 m?
8	"In the figure" In the figure: a box moves on a frictionless surface through a displacement d = -3 i m. The wind is acting on the box by force F = (2 i – 6 j) N, a) How much work does F do during the displacement? b) If the box has a kinetic energy of 10 J at the beginning of the displacement, what is the kinetic energy at the end.
9
10	Work done by a Gravitational Force
11	"An initially stationary crate in..." An initially stationary crate in is pulled, via a cable, a distance L = 5.70 m up a frictionless ramp, to a height h of 2.50 m where it stops. a) How much work W_g is done on the crate by the gravitational force F_g during the lift? b) How much work W_T is done on the crate by the force T from the cable during the lift?
12
13	"An elevator cab of mass..." An elevator cab of mass m=500kg Is descending with speed v_i = 4.0 m/s when Its supporting cable begins to slip, allowing it to fall with constant acceleration a = g/5 a) During the fall through a distance d=12 m, what is the work W_g done on the cab by the gravitational force F_g? b) During the 12 m fall, what is the work W_T done on the cab by upward pull T of the elevator cable? c) What is the net work W done on the cab during the fall? d) What is the cab kinetic energy at the end of the 12m fall?
14	Work Done by a Spring Force
15
16	"In the figure the floor..." In the figure the floor is frictionless and the applied Force F_a = 4.9 N needed to hold the block stationary at x₁ = 12 mm. How much work does the spring force do on the block if the block is pulled rightward from x₀ = 0 to x₂ = 17 mm? Next the block is moved leftward to x₃ = -12 mm. How much work does the spring force do on the block during the displacement? Explain the sign of this work.
17	"A block of mass m..." A block of mass m = 0.40 kg slides on a horizontal frictionless table with a speed v = 0.50 m/s. It then runs into and compresses a spring of spring constant k = 750 N/m. When the block is momentarily stopped by the spring, by what distance d is the spring compressed?
18	Work Done by a General Force
19	Power P_ave = W/Δt (average power) P = dW/dt ( instantaneous power) 1 watt = 1 W = 1 J/s 1 kW-h (unit of work) P = dW/dt = F cos Φ ds /dt = F v cos Φ = F . v
20
21	"F₁ and F₂ constant forces..." F₁ and F₂ constant forces acting on the box as the box slides rightward across a frictionless floor. F₁is horizontal with magnitude 2.0 N; F₂ is applied upward by 60^o to the floor and has magnitude 4.0 N. The speed v of the box at certain instant is 3.0 m/s. What is the power due to each force acting on the box at the instant and what is the net power? Is the net power changing at that instant If the magnitude of F₂ is, instead, 6.0 N, what is the net power, and is it changing?
22
23