When jumping straight down, you can be seriously injured if you land stiff-legged. One way to avoid injury is to bend your knees upon landing to reduce the force of the impact. A 72.9-kg man just before contact with the ground has a speed of 8.74 m/s. (a) In a stiff-legged landing he comes to a halt in 1.71 ms. Find the magnitude of the average net force that acts on him during this time. (b) When he bends his knees, he comes to a halt in 0.268 s. Find the magnitude of the average net force now. (c) During the landing, the force of the ground on the man points upward, while the force due to gravity points downward. The average net force acting on the man includes both of these forces. Taking into account the directions of the forces, find the magnitude of the force applied by the ground on the man in part (b).

An ideal gas with γ=1.4 occupies 4.5 L at 300 K and 110 kPa pressure and is compressed adiabatically until its volume is 2.0 L. It's then cooled at constant pressure until it reaches 300 K, then allowed to expand isothermally back to stateA.

Find the net work done on the gas.

Find the minimum volume reached.

A circular loop in the plane of a paper lies in a 0.45 T magnetic field pointing into the paper. The loop's diameter changes from 23.0 cm to 6.8 cmin 0.54 s .

What is the magnitude of the average induced emf?

What is the average induced current if the coil resistance is 3.9 Ω ?

What is the energy needed to cause an electron to undergo a transition from the n = 4 state to the n = 5 state in hydrogen?

1. Investigate the difference between "phase velocity" and "group velocity." Why does an index of refraction of less than 1 (so v>c) not violate relativity, which says no information can move faster than the speed of light?

6. A 200-kg roller coaster reaches the top of the steepest hill with a speed of 5.80 km/h. It then descends the hill, which is at an angle of 35° and is 41.0 m long. What will its kinetic energy be when it reaches the bottom? Assume µk = 0.18.

a piece of solid lead weighing 6.5 kg at 327 degrees celsius receives 150000 joules of heat.. in what state is the lead after this occurs? the latent heat of fusion for lead is 23200 J/kg

Which of the statements regarding this situation are true? Select all that apply.

• -For a conducting sphere with a net charge Q, the electric field inside the sphere is zero and the electric field outside the sphere is the same as the field from a point charge of charge Q placed at the center of the sphere.
  

• -When one charged sphere is placed inside another the net electric field outside the larger sphere is always larger than the field due to the larger sphere alone.
  

• -When one charged sphere is placed inside another the net electric field outside the larger sphere is always non-zero.
  

• -As you move steadily out from the origin in this simulation the electric field changes smoothly. The field can never jump suddenly from one value to another.
  

• -If the outer sphere is present the electric field between its inner radius and its outer radius (inside its solid wall, in other words) is always zero.
  

• -If the outer sphere is present the way charge is distributed on the outer sphere depends only on its charge, and not on the charge of the point charge and the inner sphere.
  

• -It is possible to have no electric field inside the outer sphere and a non-zero electric field outside the outer sphere.
  

• -It is not possible to have a non-zero electric field inside the inner sphere and outside the outer sphere, but no electric field between the inner and outer spheres.
  

• -If there is a positive point charge present at the center, the field in all regions is either zero or directed away from the center.

Two ice skaters, Daniel (mass 65.0kg ) and Rebecca (mass 45.0kg ), are practicing. Daniel stops to tie his shoelace and, while at rest, is struck by Rebecca, who is moving at 13.0m/s before she collides with him. After the collision, Rebecca has a velocity of magnitude 8.00m/s at an angle of 53.1? from her initial direction. Both skaters move on the frictionless, horizontal surface of the rink.

Part A

What is the magnitude of Daniel's velocity after the collision?

Part B

What is the direction of Daniel's velocity after the collision?

Part C

What is the change in total kinetic energy of the two skaters as a result of the collision?

A cyclist turns her bicycle upside down to repair it. She then notices that the front wheel is executing a slow, small amplitude, back-and-forth rotational motion with period 12 s. Treating the wheel as a thin ring of mass 600 g and radius 30 cm, whose only irregularity is the tire valve stem, determine the mass of the valve stem.

A 50·g ice cube (at 0°C) is placed in an insulated cup with 250·g of water which is at 46°C. The latent heat of fusion for ice is 80·cal/g and the specific heat of water is 1.0·cal/g/°C.

(a) How much heat will the ice have to absorb from the water to completely melt (and turn into 0°C water)? ___ cal.

(b) Find the temperature of the 250·g of water initially at 46°C after it loses the heat required to melt the ice.? ___ °C.

(c) How much heat will the 250·g of warmer water have to transfer to the cooler water in order for its temperature to drop by 1°C? ____ cal.

(d) How much will the temperature of the 50·g of cooler water rise when it gains the heat lost by the warmer water as it cools by 1°C? ____°C.

(e) Using your results from the two previous parts, continue to follow the process of heat transfer between the warmer and cooler water until they come to equilibrium. At what temperature will they reach thermal equilibrium? _____°C.

Select all that are correct: 14. Brown Dwarfs: a. are plotted at the extreme lower left-hand corner of an HR diagram. b. are all main sequence stars. c. are actually Òfailed stars.Ó d. include Jupiter. e. are all thought to be the final evolutionary state of the lowest mass Main Sequence stars. 20. During post main sequence evolution: a. elements heavier than helium can be produced. b. the remaining lifetime is much shorter than the same star's main sequence lifetime had been. c. all stars will become extreme Population I stars in their surface spectrum. d. some stars still continue to burn hydrogen in their innermost cores. e. all stars tend to increase their masses slightly.

a box contains two halves separated by a partition. Initially, there are 3 ideal gas molecules in the left half, and a vacuum in the right half. The partiition is then removed so the gas goes through a "free expansion" so that the speeds of the molecules are unaffected. In the final state, each molecule has probability of 1/2 of being in the left half of the box and probability of 1/2 being in the right half od the box. Because each of the 3 molecules now has twice as many possible positions than before, the number of microstates of the system has increased by a factor of 2x2x2=2^3. Determine the change in entropy of the system as a result of removing the partition. (Note: We can only calculate the change in entropy of the system but not the initial and final entropy values without knowing more information) What is the probability that all three molecules will simultanesouly be in the left half of the box?

1. As the frequency goes to zero, to what value does the phase constant approach? What is expected?

2. To what value should the phase constant approach at very high (compared to the resonant frequency)?

3. Does the current lead or lag the applied voltage at very high frequency?

4. For driving frequencies below the resonant frequency, which is larger, the capacitive reactance or the inductive reactance?

5. Can any of the amplitudes VR, VL, or Vc be larger than the amplitude of the source emf E? Why or why not? One might consider an RLC phasor diagram to answer this question.

Discuss the physical principles behind lasers.