PHY 101Chapter 7

Work & EnergyPractice Problems

Summer 2013Instructor: Asad Hasan

10. An object of mass m starts from rest and slides a distance d down a frictionless incline of angle . While sliding, it contacts an unstressed spring of negligible mass as shown in Figure P8.10. The object slides an additional distance x as it is brought momentarily to rest by compression of the spring (of force constant k). Find the initial

separation d between object and spring. .

See also Bridging problem page 231; chapter 7

13. Two objects are connected by a light string passing over a light frictionless pulley as shown in Figure P8.13. The object of mass 5.00-kg is released from rest. Using the principle of conservation of energy, (a) determine the speed of the 3.00-kg object just as the 5.00-kg object hits the ground. (b) Find the maximum height to which the 3.00-kg object rises. a) v = 4.43 m/s, b) yamx = 5m

24. A particle of mass m = 5.00 kg is released from point A and slides on the frictionless track shown in Figure P8.24. Determine (a) the particle's speed at points B and C and (b) the net work done by the gravitational force in moving the particle from A to C.

31. The coefficient of friction between the 3.00-kg block and the surface in Figure P8.31 is 0.400. The system starts from rest.

a) What is the speed of the 5.00-kg ball when it has fallen 1.50 m? v=3.74 m/s

b) What is the acceleration of the 5.00-kg ball when it has fallen 1.50 m?

to determine the acceleration use ; a = 4.66 m/s2

36. A 50.0-kg block and 100-kg block are connected by a string as in Figure P8.36. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between the 50-kg block and incline is 0.250. Determine the change in the kinetic

energy of the 50-kg block as it moves from A to B, a distance of 20.0 m. .

48. A block slides down a curved frictionless track and then up an inclined plane as in Figure P8.48. The coefficient of kinetic friction between block and incline is k. Use energy methods to show that the maximum height reached by the block is

ymax

h1 k cot

54. A 2.00-kg block situated on a rough incline is connected to a spring of negligible mass having a spring constant of 100 N/m (Fig. P8.54). The pulley is frictionless. The block is released from rest when the spring is unstretched. The block moves 20.0 cm down the incline before coming to rest. Find the coefficient of kinetic friction between

block and incline.

57. A 10.0-kg block is released from point A in Figure P8.57. The track is frictionless except for the portion between points B and C , which has a length of

6.00 m. The block travels down the track, hits a spring of force constant 2 250 N/m, and compresses the spring 0.300 m from its equilibrium position before coming to rest momentarily. Determine the coefficient of kinetic friction between the block and the rough surface between B and C.k = 0.328