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Two people sit opposite each other on the edge of a rotating disk of radius, R, and negligible mass. One person has a mass of 40kg, the other of 50kg. The disk is rotating at 30 revs/min. What is the rotational kinetic energy if R=1.5m?

Rotational Kinetic Energy (KE) = (1/2) x Moment of Inertia (I) x (Angular Velocity (w) ) 2 I=SUM(MR 2 ) = 40 x (1.5) 2 + 50 x (1.5) 2 = 90 x (1.5) 2 = 202.5 kgm 2 w= 30 revs / min = 30 x (2π/60) = π (rad/s)K...
JS
Answered by Joe S. • Physics tutor
2290 Views

Light with a frequency of 200nm is shone on a sodium plate with a work function of 2.28eV and electrons start escaping the surface of the plate due to the photoelectric effect. What is the maximum kinetic energy of one of these electrons in eV?

The work function of a metal is the minimum amount of energy required for electrons to start escaping the surface. This means that if we calculate the energy of each photon from the light and subtract the wo...
RS
Answered by Robert S. • Physics tutor
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Bernard says that a mass executing uniform circular motion is not accelerating as it's speed is not changing. Which parts of his statement are correct and which are false. For those which are false state why they are and give the correct version.

Correct:For a mass which is executing uniform circular motion, it's speed doesn't change. False:(1) A mass which is executing uniform circular motion is not accelerating Correction to (1) Acceleration is def...
OC
Answered by Oliver C. • Physics tutor
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An electron moving at 1000 m/s annihilates with a stationary positron. What is the frequency of the single photon produced?

The first thing to be aware of is that the frequency of a photon will depend on two things, its wavelength (c=fλ ) and its energy (E=hf). There is no information regarding the wavelength of the photon, but w...
LM
Answered by Lawrence M. • Physics tutor
2728 Views

A cannon is fired at 30 degrees from the ground and the cannonball has initial velocity of 15 m/s. What is the height of the highest point the cannonball reaches and how far is this point horizontally from the cannon?

With this type of question always draw a diagram with the values on it. We can assume the positive direction is upwards. Start with considering the vertical motion and use SUVAT. s= ? (this is what we are lo...
EV
Answered by Elena V. • Physics tutor
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