On a trip, a family travels 200 km in 2.5 h on the first day, 300 km in 4.0 h on the second day, and 250 km in 3.5 h on the third day. What was the average speed, in kilometers per hour, for the total trip?


75 km/h

Physics & Space Science

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When can Sirius, a favorite star of the Northern Hemisphere, be observed?

a. during summer b. during spring c. all year long d. during winter e. during fall

Physics & Space Science

including a contact resistance of 0.1 K/W at each of the interfaces. but assume that instead of surface temperatures, the given temperatures are those of air on the left and right sides of the wall and that the convective heat transfer coefficients on the left and right surfaces are 6 and 10 W/(m2K), respectively.

GIVEN
• Composite wall
• Thermal conductivities
? kA = 70 W/(m K)
? kB = 60 W/(m K)
? kC = 40 W/(m K)
? kD = 20 W/(m K)
• Air temperatures
? Left side (TA?) = 200°C
? Right side (TD?) = 50°C
• Contact resistance at each interface (Ri) = 0.1 K/W
• Convective heat transfer coefficients
? Left side ( cA h ) = 6 W/(m2 K)
? Right side ( cD h ) = 10 W/(m2 K)
FIND
(a) Rate of heat transfer through the wall (q) (b) Temperatures at the interfaces
ASSUMPTIONS
• One dimensional, steady state conduction
SKETCH

Physics & Space Science

Find the magnetic force when a charge 3.5C with flux density of 4 units is having a velocity of 2m/s.

a). 14. b). 28. c). 7. d). 32.

Physics & Space Science

A block is projected with speed v across a horizontal surface and slides to a stop due to friction. The same block is then projected with the same speed v up an incline where is slides to a stop due to friction. In which case did the total mechanical energy of the block decrease the least?

a. This problem cannot be solved since it was not indicated whether the horizontal surface and the incline both had the same coefficient of kinetic friction. b. The case on the horizontal surface had the least decrease in total mechanical energy. c. The case on the inclined surface had the least decrease in total mechanical energy. d. In both cases the decrease in mechanical energy was the same.

Physics & Space Science