The length of a certain wire is doubled while the radius is reduced by a factor of 4. What is the change in the resistance of this wire?
A) It stays the same.
B) It is quadrupled.
C) It is increased by a factor of 32.
D) It is increased by a factor of 16.
E) It is increased by a factor of 8.
C
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Dimensional Analysis: The gravitational force of attraction F between two tiny masses m1 and m2 that are separated by a distance r is F = G 
. In the SI system, force has units of kg ? m/s2 . Use the given gravitational force formula to determine the SI units of G in terms of the fundamental quantities of mass, length, and time.
Fill in the blank(s) with the appropriate word(s).
A 310-g air track cart is traveling at 1.25 m/s and a 260-g cart traveling in the opposite direction at 1.33 m/s. What is the speed of the center of mass of the two carts?
A) 1.47 m/s B) 1.29 m/s C) 0.131 m/s D) 0.0732 m/s E) 2.80 m/s
A long solenoid (1000 turns/m) carries a current of 25 mA and has an inside radius of 2.0 cm. A long wire which is parallel to and 4.0 cm from the axis of the solenoid carries a current of 6.0 A. What is the magnitude of the magnetic field at a point on the axis of the solenoid?
a. 51 ?T b. 61 ?T c. 43 ?T d. 81 ?T e. 1.4 ?T
A space station out beyond the solar system is rotating with constant angular velocity. A spaceship heading into the station along a diameter of the station, uses its rockets to brake, and then docks inside the station at its center. When the spaceship docks, the angular momentum of the system consisting of the station and ship
a. is less than the original angular momentum of the station. b. is the same as the original angular momentum of the station. c. is greater than the original angular momentum of the station. d. is less than the original angular momentum of the station, but the angular velocity increases. e. is greater than the original angular momentum of the station, but the angular velocity decreases.