When you drag a toy teddy bear along the floor by a force that is parallel to the floor, the magnitude of the force of friction
A. is independent of velocity or acceleration.
B. increases when the velocity increases.
C. is proportional to the acceleration.
D. decreases when the force parallel to the floor increases.
E. increases when the force parallel to the floor increases.
Answer: A
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To more accurately model the energy input from the sun, suppose the absorbed flux in given by qabs (t) = t (375 – 46.875 t) where t is in hours and qabs is in W/m2. (This time variation of qabs gives the same total heat input to the wall i.e., 2000 W hr/m2). for qabs in place of the constant value of 500 W/m2. Explain your results. A Trombe wall is a masonry wall often used in passive solar homes to store solar energy. Suppose that such a wall, fabricated from 20-cm-thick solid concrete blocks (k = 0.13 W/(mK), ? = 0.05 × 10–5 m2/s) is initially at 15°C in equilibrium with the room in which it is located. It is suddenly exposed to sunlight and absorbs 500 W/m2 on the exposed face. The exposed face loses heat by radiation and convection to the outside ambient temperature of
–15°C through a combined heat transfer coefficient of 10 W/(m2 K). The other face of the wall is exposed to the room air through a heat transfer coefficient of 10 W/(m2 K). Assuming that the room air temperature does not change, determine the maximum temperature in the wall after 4 hours of exposure and the net heat transferred to the room. GIVEN • Trombe wall with specified absorbed solar flux as a function of time FIND (a) Maximum temperature in the wall after 4 hours (b) Heat input to the room
What is the "chicken-and-egg" type problem we face when trying to decide which came first–proteins or nucleic acids?
A) proteins and nucleic acids probably looked very different before the origin of life B) nucleic acids cannot replicate without proteins, and proteins cannot be made without nucleic acids C) early proteins and nucleic acids were very similar to each other D) proteins and nucleic acids are always present together at the same time
Which of the following radiations has the greatest frequency?
a. Infrared b. Visible c. Ultraviolet d. X-rays
An astronomical telescope is made with lenses of focal lengths 80.0 and 1.25 cm. What magnifying power does this telescope provide?
A. 10 B. 81 C. 79 D. 64 E. 41