Density gravity and buoyancy The wood block with density of 0.6 × 10 and volume of 0.0001 m3 was put into crude oil The wood floats on the oil surface. One third of the volume is outside the oil surface Calculate the buoyancy of wood block (G is 10N / kg) If the volume of a barrel of oil is one sixth of a cubic meter, how many barrels is one ton of crude oil equal to

Density gravity and buoyancy The wood block with density of 0.6 × 10 and volume of 0.0001 m3 was put into crude oil The wood floats on the oil surface. One third of the volume is outside the oil surface Calculate the buoyancy of wood block (G is 10N / kg) If the volume of a barrel of oil is one sixth of a cubic meter, how many barrels is one ton of crude oil equal to

Because it floats, the gravity on the block is equal to the buoyancy of the liquid on it
F = g wood = mg = ρ V g = 0.6 * 10 ~ 3kg / m3 * 0.0001 m3 * 10N / kg = 0.6N
F floating = ρ oil g V discharge
So ρ oil = f floating / g V row = 0.6 n / (10 N / kg * 0.0001 * two thirds) = 0.9 * 10 ~ 3 kg / m3
The volume of 1 ton crude oil is v = m / ρ oil = 1000 kg / 0.9 * 10 ~ 3 kg / m3 = 10 / 9 m3
Number of barrels n = vtotal / V one barrel = 10 / 9 cubic meters divided by 1 / 6 cubic meters = 20 / 3 barrels

If there is only gravity and buoyancy, how can we measure the volume and density of an object

According to the gravity formula g = mg, the mass of the object can be calculated, and then according to the buoyancy of the object in the liquid, the liquid is preferably water, because the density of water is 1000kg / m ^ 3, f = PGV, so the volume can be calculated. According to the mass calculated in the previous step, the density can also be obtained, but the precondition for doing so is that the physics must be completely immersed in the liquid~

What's the way to get approximate numbers

There are three,
Extreme value
Normalization method
rounding

There is a railway bridge with a length of 1000 meters. A train passes through the bridge. It takes 120 seconds for the train to get on the bridge and get off the bridge completely. The time for the whole train to be completely on the bridge is 80 seconds. What are the speed and length of the train?

Let the speed of the train be x m / s and the length of the train body be y m, and the relationship between them is listed. The equations are 120x = 1000 + y, ①, 80x = 1000-y, ②, which are solved by ① and ②: x = 10 m, y = 200 m. a: the speed and length of the train are 10 m / s and 200 m respectively

It is known that the circumference of a rectangle is 40 cm, the length is x cm, and the width is ()
A.（40-x）cm B.（20-x）cm C.(40-2x) cm D.x/40-x cm
I think it should be: 2 / 40-2x cm, but not as soon as possible

It is known that the circumference of a rectangle is 40 cm, the length is x cm, and the width is (b)
A.（40-x）cm B.（20-x）cm C.(40-2x) cm D.x/40-x cm

If m power of a = 4, n power of a = 3., then 2m + 3N power of a = thank you,

2m + 3N power of a = 2m power of a × 3N power of a = (m power of a) × (n power of a) = 4 × 3 = 16 × 27 = 432

If it's more than 3 minutes, it's 0.5 yuan. If it's more than 3 minutes, it's 0.3 yuan for every more than 1 minute?

3 + (1.7-0.5) △ 0.3 = 3 + 1.2 △ 0.3 = 3 + 4 = 7 (minutes); a: he called for 7 minutes

In rectangular paper ABCD, ab = 3, ad = 5. As shown in the figure, fold the paper so that point a falls at a 'on the edge of BC, and the crease is PQ. When point a' moves on the edge of BC, the end point P.Q of the crease also moves. If the limiting points P and Q move on the edge of AB and ad respectively, the maximum distance that point a 'can move on the edge of BC is ()
A. 1B. 2C. 3D. 4

As shown in Figure 1, when point d coincides with point Q, according to the folding symmetry, we can get a ′ d = ad = 5. In RT △ a ′ CD, a ′ D2 = a ′ C2 + CD2, that is 52 = (5-a ′ b) 2 + 32, we can get a ′ B = 1. As shown in Figure 2, when point P coincides with point B, according to the folding symmetry, we can get a ′ B = AB = 3, ∵ 3-1 = 2, and the maximum distance that a ′ can move on the edge of BC is 2

Xiao Lin bought two erasers and three pencils for three yuan and four jiao; Xiao Ming bought the same two erasers and five pencils for five yuan, one eraser and one pencil for each?
To have horizontal, add the above: how much is each?

5-3 = 2 pencils 5-3.4 = 1.6 yuan in total
1.6 △ 2 = 0.8 yuan per pencil
Each rubber (5-0.8 × 5) △ 2 = 0.5 yuan

According to the regulations, taxis in a city charge 7 yuan at the starting price within 3 kilometers (including 3 kilometers), 2 yuan and 4 jiao per kilometer for more than 3 kilometers. One day, Xiao Ming's family took a taxi to the sun palace, paying 16 yuan and 6 jiao in total. How far is Xiao Ming's home from the sun palace?

(16.6-7) △ 2.4 + 3 = 9.6 △ 2.4 + 3, = 4 + 3, = 7 (km). A: Xiaoming's house is 7 km away from Taiyanggong