A fully loaded, slow-moving freight elevator has a cab with a total mass of 1500 kg, which is required to travel upward 45 m in 1.1 min, starting and ending at rest. The elevator's counterweight has a mass of only 920 kg, so the elevator motor must help pull the cab upward. What average power is required of the force the motor exerts on the cab via the cable? Number Units

A fully loaded, slow-moving freight elevator has a cab with a total mass of 1500 kg, which is required to travel upward 45 m in 1.1 min, starting and ending at rest. The elevator's counterweight has a mass of only 920 kg, so the elevator motor must help pull the cab upward. What average power is required of the force the motor exerts on the cab via the cable? Number Units

Physics for Scientists and Engineers, Technology Update (No access codes included)

9th Edition

ISBN:9781305116399

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter8: Conservation Of Energy

Section: Chapter Questions

Problem 8.38P: A 650-kg elevator starts from rest. It moves upward for 3.00 s with constant acceleration until it...

See similar textbooks

Similar questions

The system shown in Figure P5.43 is used to lift an object of mass m = 76.0 kg. A constant downward force of magnitude F is applied to the loose end of the rope such that the hanging object moves upward at constant speed. Neglecting the masses of the rope and pulleys, find (a) the required value of F, (b) the tensions T1, T2, and T3, and (c) the work done by the applied force in raising the object a distance of 1.80 m. Figure P5.43
Review. The mass of a car is 1 500 kg. The shape of the cars body is such that its aerodynamic drag coefficient is D = 0.330 and its frontal area is 2.50 m2. Assuming the drag force is proportional to v2 and ignoring other sources of friction, calculate the power required to maintain a speed of 100 km/h as the car climbs a long hill sloping at 3.20.
Two blocks, A and B (with mass 50.0 kg and 1.00 102 kg, respectively), are connected by a string, as shown in Figure P5.86. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between block A and the incline is k = 0.250. Determine the change in the kinetic energy of block A as it moves from to , a distance of 20.0 m up the incline (and block B drops downward a distance of 20.0 m) if the system starts from rest. Figure P5.86
(a) How long would it takea 1.50105 -kg airplane with engines that produce 100 MW of power to reach a speed of 250 m,/s and an altitude of 12.0 km if air resistance were negligible? (b) If it actually takes 900 s, what is the power? (c) Given this power, what is the average force of air resistance if the airplane takes 1200 s? (Hint: You must find the distance the plane travels in 1200 s assuming constant acceleration.)
A light spring with spring constant 1.20 103 N/m hangs from an elevated support. From its lower end hangs a second light spring, which has spring constant 1.80 103 N/m. A 1.50-kg object hangs at rest from the lower end of the second spring, (a) Find the total extension distance of the pair of springs, (b) Find the effective spring constant of the pair of springs as a system. We describe these springs as being in series. Hint: Consider the forces on each spring separately.
Suppose you are reshelving books in a library. As you lift a book from the floor and place it on the top shelf, two forces act on the book: your upward lifting force and the downward gravity force. (a) Is the mechanical work done by your lifting force positive, zero, or negative? (b) Is the work done by the gravity force positive, zero, or negative? (c) Is the sum of the works done by both forces positive, zero, or negative?
A sprinter of mass m accelerates uniformly from rest to velocity v in t seconds. (a) Write a symbolic expression for the instantaneous mechanical power P required by the sprinter in terms of force F and velocity v. (b) Use Newtons second law and a kinematic equation for the velocity at any time to obtain an expression for the instantaneous power in terms of m, a, and t only. (c) If a 75.0-kg sprinter reaches a speed of 11.0 m/s in 5.00 s, calculate the sprinters acceleration, assuming it to be constant. (d) Calculate the 75.0-kg sprinters instantaneous mechanical power as a function of time t and (e) give the maximum rate at which he burns Calories during the sprint, assuming 25% efficiency of conversion form food energy to mechanical energy.
. A particular hydraulic pile driver uses a ram with a mass of 1040 kg. If the maximum pile energy is 11,780J, how high must the ram he raised to achieve this value? Assuming it takes 0.62 s for the pile driver’s winch motor to raise the ram at a constant speed to this height, what is the power output by the motor in completing this task? Express your answer in both watts and horsepower.
A 650-kg elevator starts from rest. It moves upward for 3.00 s with constant acceleration until it reaches its cruising speed of 1.75 m/s. (a) What is the average power of the elevator motor during this time inter-val? (b) How does this power compare with the motor power when the elevator moves at its cruising speed?
(a) A child slides down a water slide at an amusement park from an initial height h. The slide can be considered frictionless because of the water flowing down it. Can the equation for conservation of mechanical energy be used on the child? (b) Is the mass of the child a factor in determining his speed at the bottom of the slide? (c) The child drops straight down rather than following the curved ramp of the slide. In which case will he be traveling faster at ground level? (d) If friction is present, how would the conservation-of-energy equation be modified? (e) Find the maximum speed of the child when the slide is frictionless if the initial height of the slide is 12.0 m.
For each of the situations given, state whether frictional forces do positive, negative, or zero work on the italicized object. (a) A plate slides across a table and is brought to rest by friction. (b) A person pushes a chair at constant speed across a rough, horizontal surface. (c) A box is set down on a stationary conveyor belt. The conveyor belt is then turned on and the box begins to move, being carried along by the belt. (d) A person exerts a horizontal force on a banana at rest on a counter top. The banana remains at rest.
(a) Find the useful power output of an elevator motor that lifts a 2500-kg load a height of 35.0 m in 12.0 s, if it also increases the speed from rest to 4.00 m/s. Note that the total mass of the counterbalanced system is 10,000 kg—so that only 2500 kg is raised in height, but the full 10,000 kg is accelerated. (b) What does it cost, if electricity is $0.0900 per kW h?