The temperature coefficient of resistivity of iron is 5.0 x 10-3 /oC; that of carbon is -0.50 x 10-3 /oC. When an iron wire and a carbon rod, each having the same 10 resistance at 20 oC, are cooled from that temperature to -80 oC, the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is

1. -0.10.
2.+;2.1.
3. -10.
4. +;1.9.
5.+;10.

Ahollow metal sphere has 6 cm and 11 cm inner and outer radii, respectively. the surface charge density on the inside surface is −100nc/m2. the surface charge density on the exterior surface is:

Arunner is jogging at a steady 3.6 km/hr. when the runner is 2.9 km from the finish line, a bird begins flying from the runner to the finish line at 14.4 km/hr (4 times as fast as the runner). when the bird reaches the finish line, it turns around and flies back to the runner. even though the bird is a dodo, we will assume that it occupies only one point in space, i.e., a zero-length bird. how far does the bird travel? (b) after this first encounter, the bird then turns around and flies from the runner back to the finish line, turns around again and flies back to the runner. the bird repeats the back and forth trips until the runner reaches the finish line. how far does the bird travel from the beginning? (i.e. include the distance traveled to the first encounter)

Acar travels in reverse. it covers 150 meters in 12 seconds what is the velocity of the car what is the speed of the car