A 2.20-m radius playground merry-go-round has a mass of 101.5 kg and is rotating with an angular velocity of 0.91 rev/s. What is its angular velocity after a 38.4-kg child gets onto it by grabbing its outer edge? The child is initially at rest. Express your answer in revs/s.

A series of whole-body counts indicated that a worker had a body burden of 18 microCi of Na-24 which was cleared from his body with effective half-life of 12 hours. Calculate: a. The biological half-life b. Cumulative activity c. Dose to the whole body

a) What is the greatest possible geocentric latitude of Venus, i.e., how far from the Sun can the planet be at the inferior conjunction? Assume the orbits are circular. b) When is the situation possible? The longitude of the ascending node of Venus is 77◦ .

A uniform plank of mass M and length L leans against a vertical wall. The initial angle it makes with the horizontal ground is 60º. It is let go from rest and slides down frictionlessly. The moment it leaves contact with the wall, what angle does it make with the ground? There is no friction anywhere.

A heat engine uses a heat source at 580 ∘C and has an ideal (Carnot) efficiency of 29 % .

To increase the ideal efficiency to 46 % , what must be the temperature of the heat source?

Is work done when dragging a mass up a hill the same as the change in potential energy?

Is work the same as energy? I am confused as to why

The pV diagram in (Figure 1) shows a cycle of a heat engine that uses 0.250 mole of an ideal gas having γ=1.10. The curved part ab of the cycle is adiabatic. The internal energy of the gas changes by the following amounts: ΔUa→b=−2220J, ΔUb→c=−1.06×104J, and ΔUc→a=+1.29×104J. c=(0.002, 1.5) b=(0.009, 1.5)

Part A: Find the pressure of the gas at point a.

Express answers in pascals to three significant figures.

Part B: How much heat enters this gas per cycle?

Express your answer in joules to three significant figures.

Part D: How much heat leaves this gas in a cycle?

Express your answer in joules to three significant figures.

Part F: How much work does this engine do in a cycle?

Express your answer in joules to three significant figures.

What is the effective dose from 0.050 Ci of 210₈₄Po that is ingested that is ingested by a 70 kg person? Assume an exposure time of 24 hours. 210₈₄Po decays to the stable isotope 206₈₂Pb by alpha emission. Since the exposure is much shorter than the half-life, you can assume that the activity remains constant. Alpha particles have an RBE of 20.

A chunk of brass with mass 0.6 kg, with specific heat 380 J/(kg· K), and with temperature 400 K is placed in 0.6 kg of water, with specific heat 4186 J/(kg· K), and with temperature 280 K. The water and the brass are in an insulated container and come to thermal equilibrium. Find the final temperature in kelvins (closest answer).

AND

The asteroid Oumuamua observed this year in November traveled around the sun at a speed of 87,500 m/s. Its proper length is 180 m. How much does a stationary observer near the sun measure its length to be changed at this speed due to relativity? A positive answer means its length is measured to be increased and a negative answer means that its length is measured to be decreased. (In micrometers, closest answer.)

AND

A radioactive sample is measured to be emitting 200 alpha particles per second. 20 minutes later it is emitting only 126 alpha particles per second. The half life of the unstable nucleus that is emitting these particles is - (in minutes, closest answer)

Two point charges are placed on the x axis as follows: Charge q1 = 4.00nC is located at x = 0.200m , and charge q2 = 5.00nC is at x=?0.300m. What are the magnitude and direction of the net force exerted by these two charges on a negative point charge q3 = -0.600nC placed at the origin?

A. magnitude

B. direction

Find the moment of inertia of a circular disk of radius R and mass M that rotates on an axis passing through its center. [Answer: ½ MR2]
Step 1: Pictorial representation: Sketch a neat picture to represent the situation.

Step 2: Physical representation: 1) Cut the disk into many small rings as it has the circular symmetry. 2) Set up your coordinate system and choose its origin at the pivot point (or the axle location) for convenience. Then choose a not-special piece as a representative of those small masses dm:



Step 3: Determine the moment of inertia of this representative small mass and evaluate the integral for the total moment of inertia:










Step 4: Use the parallel-axis theorem to determine the moment of inertia of the disk around an axis located at the edge of the disk. Then compare the two moments of inertia and explain how the results make sense to you.

Why hʋ is greater than energy gap in some material and µe usually greater than µh (µe is electron mobility , µh mobility of holes)?