A 60.0-kg person rides in an elevator while standing on a scale. The scale reads 400 N. The acceleration of the elevator is closest to
A) 3.13 m/s2 downward.
B) 6.67 m/s2 downward.
C) zero.
D) 9.80 m/s2 downward.
E) 6.67 m/s2 upward.
A
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A large slab of steel 0.1-m-thick contains a 0.1-m-diameter circular hole, whose axis is normal to the surface. Considering the sides of the hole to be black, specify the rate of radiative heat loss from the hole. The plate is at 811 K, the surroundings are at 300 K.
GIVEN
• A large slab of steel with a hole whose axis is normal to the surface
• Slab thickness (S) = 0.1 m
• Hole diameter (D) = 0.1 m
• Plate temperature (T1) = 811 K
• Temperature of surrounding (T?) = 300 K
FIND
• The rate of radiative heat loss from the hole (qr)
ASSUMPTIONS
• The sides of the hole are black
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 120 V. What is the power output of the secondary coil?
A) 30 W B) 120 W C) 480 W D) 960 W E) need more information
An object of mass m is moving on a horizontal rough surface. At a certain point it has a speed v m/s and it comes to a stop after traveling 32 m
If the coefficient of friction between the object and the surface is 0.40, what is the value of speed v? Use g = 10 m/s2. A) 16 m/s B) 26 m/s C) 32 m/s D) 38 m/s E) 10 m/s
A carbon dioxide laser emits photons of 10.6 ?m wavelength. How many photons per second are emitted by a 10.0 kW CO2 laser?
a. 
b. 
c. 
d. 
e. 