A 6.0-kg block slides along a horizontal surface. If µk = 0.20 for the block and surface, at what rate is the friction force changing the mechanical energy of the block at an instant when its speed is 4.0 m/s?
a. ?59 W
b. ?47 W
c. ?71 W
d. ?82 W
e. +71 W
b
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A stonecutter's chisel has an edge area of 0.7 cm2 . If the chisel is struck with a force of 42 N, what is the pressure exerted on the stone?
a. 600 N/m2 b. 30,000 N/m2 c. 300,000 N/m2 d. 600,000 N/m2 e. 6000 N/m2
What is the basic explanation for the origin of electromagnetic waves?
A cube of material with emissivity of 0.4 is heated from room temperature of 20°C to 100°C. The net power radiated by the cube is 20 W. What is the volume of the cube? (? = 5.6696 × 10^–8 W/m2·K4
a. 0.0014 m3 b. 0.012 m3 c. 0.11 m3 d. 1.8 m3
Suppose we know the value of 
for a simple harmonic oscillator. What further information do we need to know to fix the amplitude A and the initial phase ? in the solution to the simple harmonic oscillator equation? (If more than one item is needed, feel free to indicate more than one answer.)
A. The oscillating object’s initial position B. The oscillating object’s initial velocity C. The object’s mass D. The oscillation’s period E. The spring’s spring constant F. We do not need additional information. G. The oscillating object’s initial(position+velocity)