Test7Spring2022
.pdf
School
Mesa Community College**We aren't endorsed by this school
Course
PHY 280
Subject
Physics
Date
Dec 19, 2024
Pages
4
Uploaded by ColonelClover9677
Bergen Community College PHY-280 Physics I Dr. Sivo Test 7 005LS 4/19/2022Chapter 7 - Kinetic Energy and Work(Work and Kinetic Energy, Kinetic Energy, Work-Kinetic Energy Theorem) 1. (20 pts total)As shown in Figure 1, a mass = kg is initially moving in a horizontal -plane. Two constant forces of magnitudes = 100.0 N and = 125.0 N then begin to act on the mass as the mass continues to move through a displacement of magnitude = 5.00 m. The angles of the forces measured counterclockwise with respect to the positive axis are = 20.0and = 60.0, respectively. No other forces act on the mass. The angle of the displacement measured counterclockwise with respect to positive axis is = 40.0. a)(10 pts) Using the definition of work for constant forces, calculate the net work done by the above forces. b)(10 pts) If the magnitude of the initial velocity of the mass was = 20.0 m/s when the forces began to act, calculate the magnitude of the final velocity of the mass when it has move through the above displacement. Make use of your answer to1aand the Work-Kinetic Energy Theorem. Figure 1.Looking down on the horizontal -plane as two constant forces act on a mass that moves through a displacement .
(Work Done by the Gravitational Force, Work done by Lifting and Lowering an Object) 2. (20 pts total)A box is lifted by a person using a cable as shown in Figure 2 through a displacement of 10.0 m starting at rest and ending at rest. The mass of the box is 200.0 kg. Let the acceleration due to gravity be 9.8 m/s2exactly. a. (10 pts) Calculate the work that was done by gravity when the box goes through the displacement. b. (10 pts) Using your answer to 2a and the Work-Kinetic Energy Theorem, determine the work that was done by the person when the box goes through the displacement. Figure 2.Box lifted by cable.frictionless pulley frictionless pulley
(Hooke's Law, Work Done by a Spring Force, Work Done by a General Variable Force: One-Dimensional, Three Dimensional Analysis, Work-Kinetic Energy Theorem with a Variable Force, Work Calculated by Graphical Analysis) 3. (20 pts) An object of mass = 3.00 kg initially at rest (= 0.00 m/s) and located at = 0.00 m is acted on by a variable one-dimensional force in the direction. The force as a function of position is given by the graph shown in Figure 3. If this is the only force that acts on the object, use the graph to estimate the velocity of the object in the direction when the object reaches the position = 8.00 m. Make use of the Work-Kinetic Energy Theorem and your knowledge of work for a variable force. Report your answer to three significant figures. Figure 3.One-dimensional variable force as a function of position .
(Average Power, Instantaneous Power, Vehicle Top Speed) 4.(15 pts) A two-dimensional force acting on a body is given by where the component of the force is unknown. The instantaneous velocity of the body is given by . The instantaneous power provided by the force is known to be 10.0 watt. What must be the component of the force ? ( Vehicle Top Speed) 5.(15 pts) Suppose that its desired to allow a Smartcar, shown in Figure 4, to have a top speed of 200.0 mph (miles per hour). What engine power is required? Express your answer in units of horsepower. The drag coefficient of a Smartcar is 0.360. The frontal area is 2.057 m2. The density of air is 1.200 kg/m3. Solve the problem algebraically first starting with a derivation of the equation for top speed of a vehicle. Perform all unit conversions with the chain-link conversion method. You'll need to make use of the conversion relations 1 hp = 745.7 watt, 1 mi = 1.609 km, 1 h = 60 min, 1 min = 60 s, 1 km = 1000 m. Figure 4. A Smartcar.