When a balloon with mass m rises to the southwest at a constant speed, the magnitude and direction of the air action on the balloon are determined A. 0 b.mg, c.mg, D

When a balloon with mass m rises to the southwest at a constant speed, the magnitude and direction of the air action on the balloon are determined A. 0 b.mg, c.mg, D

If C is constant, the force is 0

When the balloon rises - 5 meters, it means that the balloon () is 5 meters

When the balloon goes up - 5 meters, it means that the balloon (goes down) 5 meters

Why do balloons rise?
Is it the buoyancy of the air or the different density of the gas?

Before releasing, the balloon is subject to its own gravity and air buoyancy
Self gravity = balloon gravity + hydrogen gravity in the sphere
Air buoyancy = average air density * g * balloon volume
According to Newton's second law:
Air buoyancy gravity = ma > 0
The process can also be analyzed by formula, but it is the content of University

One third of the total length of a rope is cut off in the first time, and the remaining 80% is cut off in the second time. A total of 26 meters are cut off in two times. How long is the rope?

（1-1/3）×80%=8/15
26 ÷ (1 / 3 + 8 / 15) = 30m
A: This rope is 30 meters long

Two plastic ropes, one is 80 meters long and the other is 60 meters long. If the same length is cut off from each of the two ropes, the remaining length of the short rope is that of the long rope
Five points three, how many meters to cut each of the two ropes,

80-60 = 20m
The remaining length of the short rope is the remaining 5:3 of the long rope, indicating that 20 meters is 5:2
20 / 5:2 = 50m (long rope)
80-50 = 30m
A: cut the two ropes 30 meters each

Divide a 30 meter long rope into three sections. The latter section is 3 meters more than the former. How many meters are the three sections?

30 △ 3 = 10 meters, so the middle section is 10 meters
10-3 = 7M
10 + 3 = 13m
A: the three sections are 7, 10 and 13 meters respectively

If an 80 meter long rope is cut by one eighth and then increased by one eighth, then the length of the rope is less than 80 meters. Is it right or wrong?

Correct, because 80 × (1-1 / 8) × (1 + 1 / 8) = 78.75

(1) A rope, cut 20%, just cut 3 meters. How long is this rope? (2) One rope, 20% used, 12 meters left. How long is this rope?

(1) A: the rope is 15 meters long. (2) 12 (1-20%) = 15 meters. A: the rope is 15 meters long

For two pieces of cloth of the same length, the first one takes 32 meters, and the second one takes 20 meters. As a result, the second one is three times as many meters as the first one?

According to the meaning of the question: the second piece has more meters than the first piece: 32-20 = 12 (meters); according to the difference multiple formula: the remaining meters of the first piece are: 12 (3-1) = 6 (meters); the original length of the two pieces of cloth: 6 + 32 = 38 (meters). Answer: the original length of the two pieces of cloth is 38 meters

For two pieces of cloth of the same length, the first one takes 32 meters, and the second one takes 20 meters. As a result, the second one is three times as many meters as the first one?

According to the meaning of the question: the second piece has more meters than the first piece: 32-20 = 12 (meters); according to the difference multiple formula: the remaining meters of the first piece are: 12 (3-1) = 6 (meters); the original length of the two pieces of cloth: 6 + 32 = 38 (meters). Answer: the original length of the two pieces of cloth is 38 meters