A bungee cord is essentially a very long rubber band that can stretch up to four times its unstretched length. However, its spring constant vanes over its stretch [see Menz, P.G. “The Physics of Bungee Jumping.” The Physics Teacher (November 1993) 31: 483-487]. Take the length of the cord to be along the direction and define the stretch as the length of the cord minus its un-stretched length that is, (see below). Suppose a particular bungee cord has a spring constant, for of and for. (Recall that the of (Recall that the spring constant is the slope of the force versus its stretch (a) What is the tension in the cord when the stretch is 16.7 m (the maximum desired for a given jump)? (b) How much work must be done against the elastic force of the bungee cord to stretch It 16.7 m? Figure 7.16 (credit modification of work by Graeme Churchard)

Check Your Understanding What potential energy U(x) can you substitute in Equation 8.13 that will result in motion with constant velocity of 2 m/s for a particle of mass 1 kg and mechanical energy 1 J?

A particle of mass 2.0 kg moves under the influence of the force F(x)=(3/x)N. If its speed at x=2.0 m is v=6.0 m/s, what is its speed at x = 7.0 m?

A block of mass 0.500 kg is pushed against a horizontal spring of negligible mass until the spring is compressed a distance x (Fig. P7.79). The force constant of the spring is 450 N/m. When it is released, the block travels along a frictionless, horizontal surface to point , the bottom of a vertical circular track of radius R = 1.00 m, and continues to move up the track. The blocks speed at the bottom of the track is = 12.0 m/s, and the block experiences an average friction force of 7.00 N while sliding up the track. (a) What is x? (b) If the block were to reach the top of the track, what would be its speed at that point? (c) Does the block actually reach the top of the track, or does it fall off before reaching the top?

A pendulum, comprising a light string of length L and a small sphere, swings in the vertical plane. The string hits a peg located a distance d below the point of suspension (Fig. P7.80). (a) Show that if the sphere is released from a height below that of the peg, it will return to this height after the string strikes the peg. (b) Show that if the pendulum is released from rest at the horizontal position ( = 90) and is to swing in a complete circle centered on the peg, the minimum value of d must be 3L/5. Figure P7.80

At 220 m, the bungee jump at the Verzasca Dam in Locarno, Switzerland, is one of the highest jumps on record. The length of the elastic cord, which can be modeled as having negligible mass and obeying Hookes law, has to be precisely tailored to each jumper because the margin of error at the bottom of the dam is less than 10.0 m. Kristin prepares for her jump by first hanging at rest from a 10.0-m length of the cord and is observed to stretch the rope to a total length of 12.5 m. a. What length of cord should Kristin use for her jump to be exactly 220 m? b. What is the maximum acceleration she will experience during her jump?

a) A spring with a constant of 27N/m is compressed 0.25m by a 2.0kg mass. If the spring is released the mass is shot upwards against gravity how far up will it rise? (no friction) 3. b) A sled loaded with Alice has a mass of 71kg and sits on the top of a hill with a height of 24.4m. She slides down the hill a distance of 235m with a force of friction 46N working against her. Find the velocity of the sled at the end of the run.

A spring of natural length 30 cm is attached to the floor directly below an identical spring that isattached to the ceiling. The ceiling is at a height of 3 m above the floor. A ball of mass 3 kg andradius 5 cm is projected vertically downwards with a speed of 10 m s-1from midway between the two springs.(a) If the lower spring is compressed to a length of 10 cm when the ball first comes to rest,calculate the spring constant of the springs.(b) After bouncing off the lower spring, the ball impacts the upper spring. Calculate the lengthof the upper spring when the ball comes to rest for the second time.

A toy car of mass 2.0 kg starts at the top of an incline of angle 20.°. It travels 1.0 meter down the incline to a flat surface where it encounters a spring of spring constant, k = 5.0 N/m. (a) What is the car's speed at the bottom of the incline? (b) When the car encounters the spring, by how much does it compress (max) it? (c) The spring is removed and the car now encounters a second incline as shown. What is the maximum distance the car travels up this second incline?