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Ask a physics calculation problem in grade one of senior high school A car is driving at a speed of 54km / h along a straight road at a constant speed. At a certain moment, the driver sees the red light in front of him and starts to brake. The acceleration when braking is known to be 5 / S2. As a result, the car just stops at the warning line of the red light (1) The total time that a car can move forward after braking (2) The distance from the warning line when the car starts to brake
1.t=V/a=15/5=3s
2.s=1/2at^2=0.5*5*9=22.5m
Gravitational constant G, radius r of the earth, distance r between the moon and the earth, height h of the synchronous satellite from the ground, period T1 of the moon around the earth, period T2 of the earth's rotation, acceleration g of the earth's surface, Calculation: 1. Calculate the mass of the earth according to the known conditions of the moon. 2. Calculate the mass of the earth according to the known conditions of the synchronous satellite. 3. Calculate the mass of the earth according to the objects on the surface of the earth
1)
For the moon:
GMm/r^2=4mπ^2r/T^2
The solution is m = 4 π ^ 2R ^ 3 / T ^ 2G
2) For synchronous satellites:
GMm/(h+r)^2=4mπ^2r/T2^2
The solution is m = 4 π ^ 2 (H + R) ^ 3 / T2 ^ 2G
3)
For objects:
GMm/r^2=mg
M=gr^2/G
For a car moving along a straight road with uniform speed change and straight line, it takes 3S and 2S respectively to pass through three continuous poles a, B and C. It is known that the distance between two adjacent poles is 45m, then the acceleration of the car is 0______ , passing through the middle pole at a speed of______ ．
(1) If the distance between two adjacent poles is s, then there is & nbsp; s = v1t1 + 12at21 & nbsp; 2S = V1 (T1 + T2) + 12a (T1 + T2) 2 substituting T1 = 3S, T2 = 2S, s = 45m into the solution: a = 3m / s2v1 = 10.5m/s; (2) the speed of the car passing the second pole is V2 = V1 + AT1 = 10.5 + 3 × 3 = 19.5m/s
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