12. [-/10 Points] DETAILS SERPSE10 8.5.OP.017. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A 720-N Marine in basic training climbs a 8.5-m vertical rope at a constant speed in 7.75 s. What is his power output? Need Help? Read it Watch It 13. [-/10 Points] DETAILS SERPSE10 8.5.OP.018. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER As a van travels along a level stretch of road with constant speed, most of the power developed by the engine is used to compensate for the energy transformations due to friction forces exerted on the van by the air and the road. If the power developed by the engine is 3.00 hp, calculate the total friction force acting on the van (in N) when it is moving at a speed of 32 m/s. One horsepower equals 746 W. IN Need Help? Read It 14. [-/10 Points] DETAILS SERPSE10 8.5.P.017. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER An energy-efficient lightbulb, taking in 24.0 W of power, can produce the same level of brightness as a conventional lightbulb operating at power 100 W. The lifetime of the energy-efficient bulb is 10 000 h and its purchase price is $4.70, whereas the conventional bulb has lifetime 750 h and costs $0.60 per bulb. Determine the total savings obtained by using one energy-efficient bulb over its lifetime as opposed to using conventional bulbs over the same time period. Assume an energy cost of $0.20 per kilowatt-hour. Need Help? Read It 15. [-/9.99999999999999 Points] DETAILS SERPSE10 8.5.OP.021. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A laundry uses an elevator to move items from one level to another. The elevator has a mass of 800 kg and moves upward with constant acceleration for 3.00 s until it reaches its cruising speed of 1.75 m/s. (Note: 1 hp = 746 W.) (a) What is the average power (in hp) of the elevator motor during this time interval? Pave = hp (b) What is the motor power (in hp) when the elevator moves at its cruising speed? Pcruising hp (c) What If? If the elevator motor can only deliver constant power at one setting, the amount needed for its motion at constant speed, how long (in s) will it take the elevator to accelerate to the cruising speed of 1.75 m/s? (If you need to use Do or -co, enter INFINITY or -INFINITY, respectively.) t = Need Help? Read It16. [-{10 Points] DETAILS SERPSE1O 8.A.P.026. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER As shown in the gure below, a light string that does not stretch changes from horizontal to vertical as it passes over the edge of a table. The string connects m1, a 3.80 kg block, originally at rest on the horizontal table at a height 1.25 m above the oor, to m2, a hanging 2 kg block originally a distance d = 0.970 m above the oor. Neither the surface of the table nor its edge exerts a force of kinetic friction. The blocks start to move from rest. The sliding block m1 is projected horizontally after reaching the edge of the table. The hanging block m2 stops without bouncing when it strikes the floor. Consider the two blocks plus the Earth as the system. (a) Find the speed at which 1111 leaves the edge of the table. {Assume m2 hits the ground before m1 leaves the table.) {1 "1'5 (b) Find the impact speed of oil on the oor. :Jme (c) What is the shortest length of the string so that it does not go taut while m1 is in ight? :J m (d) Is the energy of the system when it is released from rest equal to the energy of the system just before m1 strikes the ground? 0 Yes 0 N0 (e) Why or why not? I This answer has not been graded yet. Need Help