What minimum amount of electromagnetic energy is needed to produce an electron and a positron together? A positron is a particle with the same mass as an electron, but has the opposite charge.

E=?

A cube of ice is taken from the freezer at -9.5?Cand placed in a 95-g aluminum calorimeter filled with 310g of water at room temperature of20.0 ?C. The final situation is observed to be all water at 15.0?C. The specific heat of ice is2100 J/kg?C?, the specific heat of aluminum is900 J/kg?C?, the specific heat of water is is4186 J/kg?C?, the heat of fusion of water is333 kJ/Kg. What was the mass of the ice cube?

What is centripetal acceleration? What is centripetal force? What purpose does centripetal force serve, and how can it be provided?

How far away is a star that has a parallax of 0.03 seconds of arc? 0.3 parsecs/333.3 parsecs/33.3 parsecs/3.3 parsecs

If you took a measuremnt for a stars position in March, using parallex when is the optimum month for the next measurement? Sept /Oct/ April/ any month

The nearest stars have been catalogued using parallax what is the range of the stars found in this catalogue? 4 to 100 parsecs/ 2 to 1000 parsecs/ 10 to 50 parsecs/ all stars out to 500 parsecs

Compared to close stars, the parallax angle is ________________ for more distant stars. Smaller/ larger/ the same as/ unrelated to distance of stars

Why are astronomers much more interested in the luminosity of a star than its apparent brightness? because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth/because luminosity can be measured exactly, but apparent brightness can only be roughly estimated/because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a star's chemical make

3. A rigid uniform disk (moment of inertia I = 1/2 m R²) has a mass m = 10 Kg and radius R = 2 m, it is free to rotate around a fixed axis passing through its center and is at rest at t = 0 s. A constant force F = 20 N is applied halfway between the center and the edge of the disk, in a direction perpendicular to the disk radius.

(i) Calculate the torque, the angular acceleration, the angular velocity and the rotation angle of the disk after t = 10 s. τ=20 Nm ; α=1 s^-2 ; ω=10 s^-1 ; Δθ=50 (rad)

(ii) Calculate the kinetic energy and the angular momentum of the disk at t = 10 s. K=1000 J ; L = 200 Js

(iii) Show that the relationships between torque, work, kinetic energy and angular momentum are numerically satisfied. W = τ∗Δθ = 20 Nm*50 = 1000 J ; Kf-Ki = 1000 J

τ∗Δt = 20 Nm*10s = 200 Js ; Lf-Li = 200 Js

THE ANSWERS ARE IN BOLD, COULD YOU PLEASE SHOW THE WORKING NEEDED FOR THIS QUESTION?

At what separation distance can a proton hover above another proton due to electrostatic repulsion? Hint: Compare gravity to electrostatic repulsion. Please show step by step and explain how you got the numbers. Thanks

It has been proposed that we could explore Mars using inflated balloons to hover just above the surface. The buoyancy of the atmosphere would keep the balloon aloft. The density of the Martian atmosphere is 0.0154 kg/m3 (although this varies with temperature). Suppose we construct these balloons of a thin but tough plastic having a density such that each square meter has a mass of 4.90 g. We inflate them with a very light gas whose mass we can neglect.

Part A

What should be the radius of these balloons so they just hover above the surface of Mars?

Part B

What should be the mass of these balloons so they just hover above the surface of Mars?

Part C

If we released one of the balloons from part A on earth, where the atmospheric density is 1.20 kg/m3, what would be its initial acceleration assuming it was the same size as on Mars?

two skaters collide and embrace, in a completely inelastic collision. boomer, whose mass is 83 kg, is originally moving east with v=6.2km/hr. sooner whose. mass is 55kg, is originally moving north with v=7.8km/hr. (a) what is the velocity of the couple after impact? (b) what is the velocity of the center of mass of two skaters before and aafter collision? (c) what is the fractional change in the Kinect energy of the skaters because of the collision?

An ancient club is found that contains 160 g of pure carbon and has an activity of 6.5 decays per second. Determine its age assuming that in living trees the ratio of ( 14 C 12 C ) atoms is about 1.40 × 10 − 12 . Note that the half life of carbon-14 is 5700 years and the Avogadro number is 6.02 × 10 23.

Answer in years

For what range of object positions does a bi-convex lens of focal length f form a real image?

What is the buoyant force on a helium balloon in air if the balloon is spherical with diameter 18.0 cm ?

A large rock is propelled off the edge of a cliff at an initial velocity of 14 m/s and an angle of 45

A beam of protons is accelerated through a potential difference of 0.720 kV and then enters a uniform magnetic field traveling perpendicular to the field.

A)

What magnitude of field is needed to bend these protons in a circular arc of diameter 1.79 m ?

Express your answer in tesla to three significant figures.

B)

What magnetic field would be needed to produce a path with the same diameter if the particles were electrons having the same speed as the protons?

Express your answer in tesla to three significant figures.

An electric current through hydrogen gas produces several distinct wavelengths of visible light.

a) What are the wavelengths of the hydrogen spectrum if they form first-order maximum at angles of 24.2, 25.7, 29.1 and 41.0 degrees when projected on a diffraction grating having 10,000 lines per cm?

b) What do the minimum and maximum angles become if a 1000 line-per-cm diffraction grating is used? Sketch result.

c) Discuss relationship between further reductions in lines-per-cm and the new angles for the minimum and maximum wavelengths.

d) Why is this important when designing spectroscopic experiments?

Will we someday look back on the 20th century as a time when we used an "ancient form of power transmission called electricity"? Are there better ways to carry power? Fuel pipelines? Lasers? Anything else? How important is power transmission?