91影视

^{A cubic crate of side\(s = 2.0\;{\rm{m}}\)is top-heavy: its CG is 18 cm above its true center. How steep an incline can the crate rest on without tipping over? [Hint: The normal force would act at the lowest corner].}

Question: Paper has a dielectric constant K = 3.7 and a dielectric strength of \({\bf{15 \times 1}}{{\bf{0}}^{\bf{6}}}\) V/m. Suppose that a typical sheet of paper has a thickness of 0.11 mm. You make a 鈥渉omemade鈥� capacitor by placing a sheet of \({\bf{21 \times 14}}\;{\bf{cm}}\) paper between two aluminum foil sheets (Fig. 17鈥�48) of the same size. (a) What is the capacitance C of your device? (b) About how much charge could you store on your capacitor before it would break down?

FIGURE 17鈥�48 Problem 82.

In If a 1300-kg car can accelerate from to in 3.8 s, how long will it take to accelerate from to ? Assume the power stays the same, and neglect frictional losses.

A cyclist starts from rest and coasts down a hill. The mass of the cyclist plus bicycle is 85 kg. After the cyclist has traveled 180 m, (a) what was the net work done by gravity on the cyclist? (b) How fast is the cyclist going? Ignore air resistance and friction.

A film of Jesse Owens鈥檚 famous long jump (Fig. 6鈥�47) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at at the top of the arc?

Question: A \({\bf{ + 3}}{\bf{.5}}\;{\bf{\mu C}}\) charge is 23 cm to the right of a \({\bf{ - 7}}{\bf{.2}}\;{\bf{\mu C}}\) charge. At the midpoint between the two charges, (a) determine the potential and (b) the electric field.

Water flows over a dam at the rate of and falls vertically 88 m before striking the turbine blades. Calculate (a) the speed of the water just before striking the turbine blades (neglect air resistance), and (b) the rate at which mechanical energy is transferred to the turbine blades, assuming 55% efficiency.

A 55-kg skier starts from rest at the top of a ski jump, point A in Fig. 6鈥�48, and travels down the ramp. If friction and air resistance can be neglected, (a) determine her speed when she reaches the horizontal end of the ramp at B. (b) Determine the distance s to where she strikes the ground at C.

Estimate the total mass of the Earth鈥檚 atmosphere, using the known value of atmospheric pressure at sea level.

If you stand on a bathroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 760 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?