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Explain why excited atoms only emit certain frequencies of radiation after an electron collides with the atom

Radiation is emitted via photons2) Photon energy is governed by the equation E = hc/wavelength, where h = the Planck constant and c = the speed of light. Both h and c are constants3) Electrons have discrete ...
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Answered by Michael H. • Physics tutor
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I do 400J of work compressing a gas, but I maintain the same temperature. What is the delta U, Q and W in this case?

U = 0Q = -400W = -400
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Answered by Helen C. • Physics tutor
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A trolley of mass 0.75kg is running along a frictionless track at a constant speed of 0.7ms-1, as the trolley passes below a mass of 0.5kg the mass drops a short vertical distance onto the trolley. Calculate the new velocity of the trolley and mass.

Momentum = mass x velocityInitial momentum = 0.75 x 0.7 =0.525kgms-1Momentum is assumed conserved so final momentum = 0.525kgms-1So final mass = 0.5+0.75 = 1.25kgSo final velocity = 0.525/1.25Final velocity ...
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Answered by Alexander M. • Physics tutor
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What velocity should your boat have if you want to cross a 72m wide river in 6s by the shortest distance, with a 5 m/s downstream current?

Key physics concepts: Velocity vectors, Distance/speed/time relations Key mathematical concepts: Trigonometry, Pythagorean triples, Vector addition/subtraction.Recall that velocity is a vector quantity, and ...
Answered by • Physics tutor
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A conical pendulum is a mass suspended from a point that traces out a horizontal circle. By balancing the weight with the tension in the string, determine the speed of the bob.

Draw a free-body diagram for the mass with the pendulum suspended at an angle θ to the vertical. The tension in the rope is T and the radius of the circle is r. Firstly, resolve horizontal forces and equate ...
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Answered by Daniel S. • Physics tutor
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