The Liuyang Bridge in Changsha, which was put into use only at 17, was demolished and rebuilt at the beginning of this year due to serious damage. An important cause of bridge damage is passing vehicl

The Liuyang Bridge in Changsha, which was put into use only at 17, was demolished and rebuilt at the beginning of this year due to serious damage. An important cause of bridge damage is passing vehicles. (1) Pressure of the vehicle on the road at rest:

f = G = 15× 103kg× 10N/kg = 1.5× 105n，

The pressure of the car on the road:

p = Fs = 1.5× 105n 0.3 m2 = 5× 105 pa；

(2) According to the control circuit, connect three resistors in series, and measure the voltage across R 1 with a voltmeter.

According to diagram b, when F= 1.5× 105N and Rx = 25ω,

Current in the circuit:

I = ur 1+Rx+R0 = 10v 10ω+25ω+5ω= 0.25 a，

Voltmeter indication:

u 1 = IR 1 = 0.25 a× 10ω= 2.5V；

(3) When the voltmeter indicates the maximum value, that is, U 1max=5V, the recorder can record the mass of the vehicle crossing the bridge.

Because the currents in all parts of the series circuit are equal,

So UR is always =U 1maxR 1, that is,10v10ω+r 'x+5ω = 5v10ω,

The solution is: rx'= 5ω,

According to Figure B, at this time, the pressure f ′ = 5.5×105n,

Because the pressure of the car is equal to its own gravity,

Therefore, the recorder can record the maximum mass of vehicles crossing the bridge:

m = G′G = F′G = 5.5× 105n 10N/kg = 5.5× 104kg = 55t。

Answer: (1) At rest, the pressure of the vehicle on the road surface is 5×105 Pa;

(2) In the question (1), when the vehicle crosses the bridge, the voltmeter indicates 2.5V；;

(3) The maximum mass of vehicles crossing the bridge that can be recorded by this recorder is 55t. ..