A 5.00-kg crate is sitting on the ground at rest. An electric motor with an efficiency of 0.20 (20%) is used to raise a crate up by a height of 2.0 meters so that it has an upward velocity of 4.0 m/s as it reaches that height. Calculate the electrical energy consumed by the motor during this process.
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- How much work is done by gravity when dead lifting a 100.0 kg barbell 81.54 cm from the floor to hip level ?(a) What is the efficiency of an out-of-condition professor who does 2.30 ✕ 105 J of useful work while metabolizing 510 kcal of food energy? ...........%(b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency of 15%?............ kcalKE₁ O yes (a) Is mechanical energy conserved in this problem? A 55.0-kg skier with an initial speed of 12.0 m/s coasts up a 2.50-m-high rise as shown in the figure. The coefficient of friction between her skis and the snow is 0.090. Hint: find the distance traveled up the incline assuming a straight-line path as shown in the figure. Think & Prepare O zero 1. Make note of what's given and what's unknown. Relate known quantities to symbols. 2. Draw a labeled sketch if possible. 3. Identify the physics principle and approach. Write down relevant equations symbolically. Simplify if possible. 4. Insert numerical quantities to solve for unknowns. 5. Does the answer make sense? O no (b) The change in mechanical energy equals V₁ O work done by friction. O positive. O negative. (d) Find her final speed at the top. Enter to 3 significant figures V= 35° V₁ = ? m/s 2.5 m ↓ O increase in PE. Use (b) to set-up a mathematical equation between change in mechanical energy and work done by friction (c)…
- Shoveling snow can be extremely taxing because the arms have such a low efficiency in this activity. Suppose a person shoveling a footpath metabolizes food at the rate of 800 W. (a) What is her useful power output? (b) How long will it take her to lift 3000 kg of snow 1.20 m? (This could be the amount of heavy snow on 20 m of footpath.) (c) How much waste heat transfer in kilojoules will she generate in the process?44. A metal ramp 6.00 m long is tilted 10.0° and is used to load and unload a moving van. Suppose a 20.0 kg box is pushed up the ramp and it slides with a friction coefficient of 0.30. The ramp can be viewed as a "machine" where the useful output is the potential energy gain of the box and the input is the physical work done by the person doing the pushing. (a) Determine the efficiency of the ramp. (b) Determine the ratio of the force needed to lift the box without the ramp to the force needed to push it along the ramp (this is called the mechanical advantage).A 35-kW freight elevator with a total mass of 1950 kilograms rises to a height of 25 metres in 32 seconds. What is the efficiency of the elevator? 45% 43% Option 2 Option 4 46% 44% Option 1 Option 3
- An electric elevator with a motor at the top has a cable weighing 4.5 pounds per foot.When the car is at the first floor, 180 feet of cable are out, and effectively 0 feet are outwhen the car is at the top floor. The elevator car itself weighs 2000 pounds when empty a) Find the work done by the motor lifting just the empty elevator car from the firstfloor to the top floor, ignoring the cable. b) Find the work done by the motor lifting just the cable from the first floor to the topfloor. Keep in mind, that the cable gets shorter and must therefore get lighter as theelevator goes up.Consider an elevator car (lift) with a mass of 700kg which call carry up to 600kg of passengers. Use g = 10 ms. An electric motor is used to raise the elevator with a full load from the ground floor to the third floor, 9 m higher, in 30 s. Calculate the total energy needed and the power of motor required. 12 MJ and 2kW 12400 J and 2400 W 11700 J and 3900 W 48 kJ and 2400 WMelinda is pushing a chair along a 5 meter straight path through her living room. She is standing, pushing at the top of the chair with a force of 30 newtons at a 22° angle of depression from the horizontal. (a) Calculate the work done in moving the chair. (b) How could Melinda re-arrange herself to make the energy use more efficient?
- Situation 2: A crate of mass 10.0 kg is pulled up a rough incline with an initial speed of 1.50 m/s. The pulling force is 100 N parallel to the incline, which makes an angle of 20.0° with the horizontal. The coefficient of kinetic friction is 0.400, and the crate is pulled 5,00 m. 18. Determine the increase in internal energy of the crate-incline system due to friction. 19. How much work is done by the 100-N force? 20. What is the change in kinetic energy of the crate?A 1500kg car is travelling with an initial velocity of 30.0 km/h while traveling through a school zone. Upon exiting the school zone the car accelerates to reach a speed of 65.0 km/h in 6.60 s. If the engine supplied 45.0 kW of power to do this, what is the efficiency of the engine?In a time of T seconds, a motorcycle can accelerate from rest to the speed v. (a) Determine the amount of time (in terms of 7) required for it to accelerate from v to 6v if the power output remains constant. At = (b) Determine the speed of the motorcycle (in terms of v) 3T after starting. Vf=