In proton beam therapy, a beam of high-energy protons is used to kill cancerous cells in a tumor. In one system, the beam, which consists of protons with an energy of 2.8×10−11J, has a current of 72 nA. The protons in the beam mostly come to rest within the tumor. The radiologist has ordered a total dose corresponding to 3.8×10−3J of energy to be deposited in the tumor.

Part A How many protons strike the tumor each second? Express your answer as a number of protons.

Part B: How long should the beam be on in order to deliver the required dose?

A see-saw made from 4 meter board sits on a pivot at its center. A child weighing 280 N sits 1.75 m away from the center. A second child who weighs 330 N sits on the other side such that the board remains horizontal and steady. (a) What is the torque about the pivot point due to the weight of the first child? (b) how far from the center does the second child sit? (c) What is the force (magnitude and direction) that the pivot applies to the board? Now you come and push on the end of the seesaw nearest the second child with a force of 110 N. You don’t push straight up, but at an angle of 25° from the vertical – tilted toward the center of the seesaw. The first child moves to maintain equilibrium. (d) Based on your intuition, which way should the child move? Towards or away from the center? (e) Calculate how far she is now from the center? (f) What is the force now (magnitude and direction) that the pivot applies to the board?

***Please help me with solving (e) and (f) with the equations so that I can learn how to do it. Thanks***

(1) The earth's radius is 6.37×106m; it rotates once every 24 hours.

(A) What is the speed of a point on the equator?

(2) The (Figure 1) shows two thin beams joined at right angles. The vertical beam is 13.0 kg and 1.00 m long and the horizontal beam is 28.0 kg and 2.00 m long. Neglect the lateral dimensions of the beams.

(A) Calculate the gravitational torque on the joined beams about an axis through the corner.

(3) A bowling ball is far from uniform. Lightweight bowling balls are made of a relatively low-density core surrounded by a thin shell with much higher density. A 7.0 lb (3.2 kg) bowling ball has a diameter of 0.216 m; 0.196 m of this is a 1.6 kg core, surrounded by a 1.6 kgshell. This composition gives the ball a higher moment of inertia than it would have if it were made of a uniform material. Given the importance of the angular motion of the ball as it moves down the alley, this has real consequences for the game.

(A) Compare the moments of inertia for these models by finding the ratio of Ir and Iu.

Moderating a Neutron In a nuclear reactor, neutrons released by nuclear fission must be slowed down before they can trigger additional reactions in other nuclei. To see what sort of material is most effective in slowing (or moderating) a neutron, calculate the ratio of a neutron's final kinetic energy to its initial kinetic energy, Kf/Ki, for a head-on elastic collision with each of the following stationary target particles. (Note: The mass of a neutron is m=1.009u, where the atomic mass unit, u, is defined as follows: 1u=1.66×10−27kg.) 1. An electron (M=5.49×10−4u). Express your answer using four significant figures. 2. A proton (M=1.007u). Express your answer using one significant figure. 3. The nucleus of a lead atom (M=207.2u). Express your answer using four significant figures.

Part A

Find the kinetic energy of a 1.84×10³ kg satellite in a circular orbit about the Earth, given that the radius of the orbit is 1.46×10⁴ miles.

Part B

How much energy is required to move this satellite to a circular orbit with a radius of 2.72×10⁴ miles?

4) Block 1 of mass 200 kg slides over a frictionless surface with a velocity of 0.25 cm/s and strikes block 2 of mass 100 kg sliding to the left at 0.75 cm/s. What is the final velocity of each block if the collision is

A) Perfectly elastic?

B) Perfectly inelastic?

C) If there is an external force of 4000 kg*cm/s^2 to the right for 0.008 s during the perfectly inelastic collision?

An empty rubber balloon has a mass of 0.0105 kg. The balloon is filled with helium at a density of 0.181 kg/m3. At this density the balloon is spherical with a radius of 0.300 m. If the filled balloon is fastened to a vertical line, what is the tension in the line?

You are pushing a 6·kg block across a table so that it is speeding up with an acceleration of 2·m/s².

(a) What is the net force acting on the block? ______N

(b) In addition to your push, the only other horizontal force acting on the block is friction. If your push has a magnitude of 20·N, what is the magnitude of the frictional force acting on the block?​ _______N

(c) If you want the block to stop accelerating and instead move with a constant velocity, what will the magnitude of YOUR force need to be? _______ N

-Understand the difference between mass and weight

Without altering their eating habits or exercising, what can a person do to increase or decrease their weight? Mass?

A frictionless cart of mass ? = 4.00 kg has a shape of a ramp with an incline angle ? = 60.0°. The ramp is pulled by a constant horizontal force ? = 15.0 N. Another frictionless cart of mass? = 2.00 kg can roll along the ramp and is attached to the top of the ramp at point ? by a spring of constant ? = 300. N/m. The spring is free to pivot without friction around point ?. Assume that the motion of the carts has stabilized, i.e. the top cart ? doesn’t oscillate with respectto ramp and the spring maintains a constant amount of stretch. Find acceleration of the carts, normal force between the carts and the amount of stretch of the spring.

Please can you do it step by step, so i can understand what is going on ?

Relative humidity isn't everything. Why is it that outdoor air of 80 Fo at 55% humidity will feel more “muggy” than a 50 Fo cave at 75% humidity? What other parameter is a better measure of the actual amount of moisture in the air, and how do we define it? Then give two examples of when keeping close track of moisture in the air is important.

1. A ball of negligible size and a given mass is attached to a vertical spring that obeys Hooke's law. The mass is set in oscillation in a vertical direction. At equilibrium, its position is recorded to be "zero". At what point during the oscillation will the ball-earth-spring system have the maximum elastic potential energy?

6. In transverse waves...

A mass is moving at 10 m/s in the +x direction and it collides in a perfectly elastic collision with a mass of 4 kg moving in the -x direction. The collision takes places in 0.22 seconds and after the collision the mass that was moving in the +x direction is moving in the -x direction at 8 m/s and the mass that was moving in the -x direction is moving in the +x direction at 14 m/s. What is the magnitude of the average force, in Newtons, on the first mass which was originally moving in the +x direction before the collision?

Standard test conditions (STC) for panels are 1000 W/m²incoming radiation, panel oriented normal to the sun, and 25 °C.  If all other conditions are the same but we decrease the temperature, how will this affect power output of the panel, relative to its STC rating?  Why?

How is solar energy wasted when the frequency of incoming solar radiation is too low? When the frequency is too high?

How does a multi-junction solar cell improve efficiency compared to a single-junction cell?