A baseball pitcher loosens up his pitching arm. He tosses a 0.15-kg ball using only the rotation of his forearm, 0.32 m in length, to accelerate the ball. If the ball starts at rest and is released with a speed of 24 m/s in a time of 0.40 s, what torque is applied to the ball while being held by the pitcher's hand to produce the angular acceleration?
a. 1.1 N•m
c. 2.9 N•m
b. 11 N•m
d. 1.4 N•m
C
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The orbit of the planet Jupiter is an ellipse with the Sun at one focus. What is located at the other focus?
a. the asteroid belt b. Earth c. Saturn d. Jupiter e. nothing
Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star?
A) Pulsars are easy to identify by their almost perfectly steady periods of pulsation. B) Pulsars are very bright and therefore easy to find. C) Several pulsars are located within a dozen light-years of our solar system, making them useful for finding our solar system. D) We're pretty sure that aliens will have only radio telescopes and not optical telescopes, so they'll have a better chance of seeing pulsars than ordinary stars.
Why is a global magnetic field thought to be necessary for life to exist on the surface of a planet?
A) A magnetic field shields the planet from harmful ultraviolet light. B) A magnetic field helps form ozone in the upper atmosphere. C) A magnetic field helps keep the planet's atmosphere from being stripped away by stellar winds. D) A magnetic field helps warm the planet's surface through the greenhouse effect.
A long solenoid (radius = 3.0 cm, 2 500 turns per meter) carries a current given by I = 0.30 sin(200?t) A, where t is measured in s. When t = 5.0 ms, what is the magnitude of the induced electric field at a point which is 2.0 cm from the axis of the solenoid?
a. 7.3 × 10^?3 V/m b. 6.4 × 10^?3 V/m c. 6.9 × 10^?3 V/m d. 5.9 × 10^?3 V/m e. 8.9 × 10^?3 V/m