A 30.0-kg child sits on one end of a long uniform beam with a mass 20.0 kg and a 40.0-kg child sits on the other end. The beam balances when a fulcrum is placed below the beam a distance 1.10 m from the 30.0-kg child. How long is the beam?
A)
2.12 m
B)
1.98 m
C)
1.93 m
D)
2.07 m
E)
2.20 m
B
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Indicate whether the statement is true or false
Torque: A flat circular loop of wire is in a uniform magnetic field of 0.30 T. The diameter of the loop is 1.0 m, and a 2.0-A current flows in it. What is the magnitude of the magnetic torque on the loop when the plane of the loop is parallel to the magnetic field?
A. 0.00 N ? m B. 0.41 N ? m C. 0.47 N ? m D. 0.52 N ? m
A uniform magnetic field of 0.50 T is directed along the positive x axis. A proton moving with a speed of 60 km/s enters this field. The helical path followed by the proton shown has a pitch of 5.0 mm. Determine the angle between the magnetic field and the velocity of the proton
a.
39°
b.
51°
c.
44°
d.
34°
e.
71°
The theory of nuclear astrophysics is that all the heavy elements like uranium are formed in the interior of massive stars. These stars eventually explode, releasing these elements into space. If we assume that at the time of the explosion there were
equal amount of U-235 and U-238, how long ago did the star(s) explode that released the elements that formed our Earth? The present U-235/U-238 ratio is 0.007 0 . [The half-lives of U-235 and U-238 are 0.7 × 10^9 yr and 4.47 × 10^9 yr.]