Conceptual Physics



Physics HW #25

HW25 Questions

1.) A car has a kinetic energy of 4.32x105 J when traveling at a speed of 18 m/s. (a) What is its mass? (b) How fast would a 10 kg bowling ball have to travel to have the same energy as the car.

2.) A pinball bangs against a bumper giving the ball a speed of 26 cm/s. If the ball has a mass of 40 g, what is the ball’s kinetic energy in joules.

3.) A spoon is raised 15 cm above a table. If the spoon and its contents have a mass of 28 g, what is the gravitational potential energy associated with the spoon at that height relative to the table surface.

4.) A 75 kg skydiver is 850 m above the earth’s surface moving at 36 m/s. What is the mechanical energy of the skydiver at this point (express your answer in scientific notation).

5.) A spring lying horizontally at rest has a length of 1m. A 9.5 N force holds the spring at a new length of 1.20 m. What is the elastic energy in the spring?

6.) A spring with a spring constant of 100 N/m is attached to the ceiling and a 5 kg mass is attached to it. The stretched length of the spring is measured to be 1.75 m. What is the relaxed length of the spring.

7.) A 25 cm long spring with a force constant of 1.7 N/m is sitting on the ground in a vertical position. A mass is placed on top of the spring and it compresses it 10 cm. (a) Find the Force in the spring, (b) Find the value of the mass placed on the spring , (c) find the elastic energy in the spring

8.) A 10 cm long spring with a spring constant of 45 N/m rests horizontally and is stretched to a new length of 60 cm. Calculate the elastic potential energy in the spring

9.) The graph below, represents the relationship between vertical height and gravitational potential energy for an object near Earth’s surface. (The same graph appears in your answer booklet.)

a) Based on the graph, what is the gravitational potential energy of the object when it is 2.25 meters above the surface of Earth?

b) Using the graph, calculate the mass of the object.

c) What physical quantity does the slope of the graph represent?

d) Using a straightedge, draw a line on the graph in your answer booklet to represent the relationship between gravitational potential energy and vertical height for an object having a greater mass.

10.) A student performed an experiment in which the weight attached to a suspended spring was varied and the resulting total length of the spring measured. The data for the experiment are in the table below.

[pic]

a) Using the information in the data table, construct a graph, following the directions below.

- Plot the data points for the attached weight versus total spring length.

- Label and title your graph appropriately with units.

- Draw the line or curve of best fit.

[pic]

b) Using your graph, determine the length of the spring before any weight was attached.

c) Using your graph, determine the spring constant of the spring

ANSWERS – 1a) 2666.7 kg, b) 293.94 m/s, 2) 0.00135 J, 3) 0.0412 J, 4) 674000 J, 5) 0.95 J, m,

6) 1.26 m, 7a) 0.17 N, b) 0.017 kg, c) 0.0085 J, 8) 5.625 J, 9) 55J, 2.49 kg, weight, linear but slightly more slope, 10) be sure it’s a best fit linear line, relaxed length: extend line to x axis = 0.29 m, k = slope = 13.69 N/m

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