An iron ball with a volume of 40cm and a mass of 158g is hollow or solid. If it is hollow, what is the volume of the hollow part? Iron density (= 7.9g/cm)

(1) The total density of the ball is ρ = $- frac {m} {V} $= 158g ／ 40cm 3 = 3.96g/cm 3 = 3.96 × 10 3 kg / M 3 ＜ ρ iron, so the ball is hollow. (2) the volume of iron is m = 158g ／ 7.9g/cm 3 = 20cm 3, so the volume of hollow is 20cm 3

The density is 0.6 * 10 ^ 3kg / m ^ 3, and the volume is 2m ^ 3. The buoyancy and gravity of the wood floating on the water surface are calculated!
To use a solution to get!

The mass of wood block with density of 0.6 * 10 ^ 3kg / m ^ 3 and volume of 2m ^ 3 is 0.6 * 10 ^ 3kg / m ^ 3 × 2m ^ 3 = 1.2 * 10 ^ 3kg
G=mg=10N/kg*1.2*10^3kg=1.2*10^4N
Because 0.6 * 10 ^ 3kg / m ^ 3 is less than the density of water, buoyancy = gravity = 1.2 * 10 ^ 4N

I'm not good at English. I'd like to thank my brothers and sisters for finding some multiple choice exercises for me,

( ) 16.—How do you go to work?
—I usually go to work ______ .
A.by a car B.in a car C.on a foot D.by buses
( ) 17.—Must I finish my homework now?
—No,you ______ .
A.may not B.mustn’t C.can’t D.needn’t
( ) 18.It is a good time ______ .
A.go hiking B.to go hiking C.going hiking D.went hiking
( ) 19.— ______ do you go for a picnic?
—Three times a year.
A.How often B.How many times C.How long D.How many time
( ) 20.He’s good at ______ kung fu.
A.perform B.to perform C.performing D.performed
( ) 21.—Mum,I’ m going to Maria’ s birthday party this evening.
—______ .
A.Why not B.Good idea C.Come back early D.Have a good time
( ) 22.Joe likes ______ ,but he doesn’t like ______ this afternoon.
A.skate; skating B.skates; skating C.skating; skating D.skating; to skate
( ) 23.Her daughter was born ______ December 10,1998.
A.at B.in C.on D.during
( ) 24.It’s raining ______ outside.Please stay at home.
A.heavily B.heavy C.strong D.strongly
( ) 25.—Would you like to go for a picnic with us?
—______ ,but I’m too busy.
A.No,I can’t B.Yes,I’d love to C.I’d like D.Why not
( ) 26.—I wish you’ll have a great time.
—______ .
A.I don’t think so B.No C.Thanks a lot D.Yes
( ) 27.There’s ______ “h” in ______ word “hour” and ______ hour has sixty minutes.
A.a,the,a B.the,the,an C.an,an,a D.an,the,an
( ) 28.He has few friends in the new school,______ ?
A.does he B.isn’t he C.doesn’t he D.did he
( ) 29.—Would you like to go swimming with us?
—______ .
A.No,I don’t like B.I hate to go hiking
C.I’d love to,but I don’t feel well today D.Yes,I like
( ) 30.—Would you like ______ chocolate?
—Yes, please.And I’d like ______ water,too.
A.any,any B.some,some C.some,any D.any,some

In rectangular trapezoid ABCD, ab ‖ CD, ∠ a = 90 °, ab = 2, DC = 3, ad = 7, P is the point on ad, the triangle with P, a, B as the vertex is similar to the triangle with P, C, D as the vertex, how many p points are there? And the distance between P point and a point is calculated

In the first case, AB / DC = AP / PD, then AP = 14 / 5
Case 2 does not exist

2.25÷4/5+77.5×0.8
Simple operation,

62.1125

Why is the square root of any nonnegative number (see title) 150 reward!
Why is the sum of two numbers obtained from the square root of any nonnegative number zero?
Don't tell me, because the square root of 4 equals plus or minus 2, plus or minus 2 equals 0;
And don't tell me, because the square root of n equals the plus and minus root n, and the plus and minus root n equals 0
Tell me why the square root of n equals the plus and minus root n, and the plus and minus root n equals 0

Because two numbers with the same absolute value have the same square (power = nonnegative)
On the other hand, the absolute value of the square root of any nonnegative number is equal,
Two numbers whose absolute values are equal must be opposite to each other in this case
The sum of two opposite numbers equals 0

In quadrilateral ABCD, ab = ad, AC bisector angle BCD, AE vertical BC, AF vertical CD, it is proved that triangle Abe is equal to triangle Abe

In this case, the triangle ACB and the triangle ACD are congruent (edges and corners). So the angle B = the angle D, and the triangle ACD
In shape Abe, angle e is a right angle, and in triangle ADF, angle f is a right angle
So compare triangle Abe and triangle ADF
AB = ad, e = f, B = D
So triangle Abe is congruent with triangle ADF

The speed of a satellite is 2.88 * 10 times 7 cubic meters per hour, and that of a train is 7.5 * 10 times 4 cubic meters per hour,
How many times faster is this satellite than a train?

10-4=3
The third power of 2.88 * 10 = 2880 M / h
2880 / 7.5 = 384 times

1. Zhang Xin and Li Ming make an appointment to buy books in a book store. They can get a 20 yuan membership card and enjoy a 20% discount. Xiao Ming bought several books and saved 12 yuan with the money from the card. He asked Li Ming for the original price of the book
2. A store increases the price of a certain garment by 40% and then sells it at a 20% discount. As a result, each garment makes a profit of 10 yuan. What is the cost price of this garment?
3. Wang Qiang took part in a 3000 meter race. He ran a part of the distance at the speed of 6 meters per second and finished the rest at the speed of 4 meters per second. It took 10 minutes. How many meters did Wang Qiang run at the speed of 6 meters per second?
Will that say that mark the question number to make it clear

1. Suppose the original price is x yuan
0.8x+20+12=X
The solution is x = 160
2. Set the cost as X Yuan
（1+40%）x*0.8=x+10
The solution is x = 250 / 3
3. Set a speed of 6 meters per second for x seconds
6X+4*（600-x）=3000
The solution is x = 300
6X = 6 * 300 = 1800 (m)
A: 1800 meters

The circumference of a rectangle is 32 cm, and its length is 5 / 3 of its width. How about its area?
No algebra

Solution width x cm
x+5/3 x=32÷2
8/3 x=16
x=6
6 × 5 / 3 = 10 cm
Area: 6 × 10 = 60 square centimeter

An iron ball with a volume of 40cm and a mass of 158g is hollow or solid. If it is hollow, what is the volume of the hollow part? Iron density (= 7.9g/cm)