A lawn mower has a 6-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is
a. 1 800 J
b. 2 000 J
c. 2 200 J
d. 2 400 J
e. 2 250 J
a
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Resistors in Combination: A combination of a 2.0-? resistor in series with 4.0-? resistor is connected in parallel with a 3.0-? resistor. What is the equivalent resistance of this system?
A. 2.0 ? B. 3.0 ? C. 4.0 ? D. 9.0 ?
The first of two identical boxes of mass m is sitting on level ground. The second box is sitting on a ramp that makes a 20° angle with the ground. The normal force of the level ground on the first box is 
; the normal force of the ramp on the second box is 
. Which statement is correct?
A.
= = mg.B.
= mg; = mg sin 20°.C.
= mg; = mg cos 20°.D.
= mg; = ?mg cos 20°.E.
= ? = ?mg.One long wire carries a current of 30 A along the entire x axis. A second long wire carries a current of 40 A perpendicular to the xy plane and passes through the point (0, 4, 0) m. What is the magnitude of the resulting magnetic field at the point y = 2.0 m on the y axis?
A. 4.0 ?T B. 5.0 ?T C. 3.0 ?T D. 7.0 ?T E. 1.0 ?T
A small sphere is allowed to fall through air, and when the sphere has a speed of 4.8 × 10^–4 m/s, the viscous force on the sphere is 3.0 × 10^–15 N. If the viscosity of air is 1.4 × 10^–5 N·s/m2, what is the radius of the drop?
a. 2.4E–8 m b. 8.4E–6 m c. 2.3E–7 m d. 8.5E–7 m