The elastic energy stored in your tendons can contribute up to 35% of your energy needs when running. Sports scientists find that (on average) the knee extensor tendons in sprinters stretch 45 mm while those of nonathletes stretch only 32 mm. The spring constant of the tendon is the same for both groups, 33 N/mm. What is the difference in maximum stored energy between the sprinters and the nonathletes? Express your answer with the appropriate units. ► View Available Hint(s) AU = Submit μÀ Value Units ?

A typical muscle fiber is 2.0 cm long and has a cross-section area of 3.1 x 10-9 m2. When the muscle fiber is stimulated, it pulls with a force of 1.2 mN. What is the work done by the muscle fiber as it contracts to a length of 1.6 cm?

A Jack-in-a-box is a children's toy, where a doll (the "jack"), attached to a compressed spring, is secured in a closed box. The box is resting on a smooth horizontal surface when it is knocked over, causing the lid of the box to open. The energy stored in the spring is released and the doll is propelled out of the box along the horizontal surface. If the spring has a spring-constant 36 N/m, how much energy (in Joules) was stored in the spring if the base of the doll moves 0.9 m out of the box.

A box with with a mass m = 2kg is being pushed up a ramp by an unknown pushing force Fp. The coefficient of static friction between the box and interface is 0.7. The coefficient of kinetic friction between the box and interface is 0.6. The incline of the ramp is 15 degrees. The velocity of the box is constant. The surface of the ramp is 12 m.  What is the work done by normal force while the box is being pushed the entire length of the ramp? [ I think that it is 0 N, since the x component of normal force which is parallel to motion is 0. Is that correct?]

A trunk of mass m = 0.6 kg is pushed a distance d = 30 cm up an incline with an angle of inclination theta = 23.0° by a constant horizontal force P = 425 N (see figure). The coefficient of kinetic friction between the trunk and the incline is 0.31. P. Calculate the work done on the trunk by the applied force P. Calculate the work done on the trunk by the frictional force. Calculate the work done on the trunk by the gravitational force.

A horizontal spring attached to a wall has a force constant of k = 830 N/m. A block of mass m = 1.40 kg is attached to the spring and rests on a frictionless, horizontal surface as in the figure below. wiwwwww. x= 0 x = x;/2 x= X; (a) The block is pulled to a position x; = 6.60 cm from equilibrium and released. Find the potential energy stored in the spring when the block is 6.60 cm from equilibrium. 2.91*10**- >X Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. J (b) Find the speed of the block as it passes through the equilibrium position. 6.45 Your response differs from the correct answer by more than 100%. m/s (c) What is the speed of the block when it is at a position x/2 3.30 cm? 5.58 Your response differs from the correct answer by more than 100%. m/s

In the figure below the block has m = 3.0 kg and the spring has k = 350 N/m. If the block, initially at rest, is released from a height of 0.8 m, what is the maximum compression of the spring? Ignore friction.

A spring that has a spring constant of k = 183.0 N/m is oriented vertically, with one end on the ground. What distance y must the spring compress for an m = 2.43 kg object placed on its upper end to reach equilibrium? y = By how much AUspring does the potential energy stored in the spring increase during the compression? AUspring = J

A horizontal spring attached to a wall has a force constant of k = 870 N/m. A block of mass m = 1.30 kg is attached to the spring and rests on a frictionless, horizontal surface as in the figure below. wwwwwwwwww x= x;/2 x= x; i (a) The block is pulled to a position x; = 6.20 cm from equilibrium and released. Find the potential energy stored in the spring when the block is 6.20 cm from equilibrium. J m x = 0 (b) Find the speed of the block as it passes through the equilibrium position. m/s (c) What is the speed of the block when it is at a position x;/2 = 3.10 cm? m/s

The spring in a retractable ballpoint pen is 1.8 cm long, with a 320 N/m spring constant. When the pen is retracted, the spring is compressed by 1.0 mm. When you click the button to extend the pen, you compress the spring by an additional 5.0 mm. How much energy is required to extend the spring?