There is a correct answer to this question, and then there is the one they want you to choose. Which one should I give you first ?
Let's start with the correct answer:
The force of gravity on any object is
(mass of the object) times (acceleration of gravity on the planet where the object is) .
The acceleration of gravity on Earth is about 9.8 m/s², so the force of gravity on this object is
(4000 kg/m³) x (0.9 m³) x (9.8 m/s²)
= (3,600 kg) x (9.8 m/s²)
= 35,280 kg-m/s² = 35,280 Newtons.
That's the force of gravity attracting this block and the Earth toward each other. It makes no difference whether the block is in your bedroom closet, in the back yard under a pile of mulch, inside a steel safe resting on a bed of styrofoam peanuts and slivered almonds, or underwater in the neighbor's pool. That's the force of gravity on this block, and it's the correct answer to the question.
It's not one of the choices, though. That's because the question is poorly written. The person who wrote the question is unclear on the concepts, and the more you work with the question, the more unclear and confused YOU'LL become.
When the block is in water, the force of gravity on it doesn't change. BUT ... there's ANOTHER force on it ... the buoyant force ... acting upward on it, and canceling part of the force of gravity.
The buoyant force is the weight of the displaced water. The displaced water is the water that has to get out of the way when you drop the block in, so the volume of displaced water is the volume of the block.
-- The volume of the block is (0.9 m³).
-- The density of water is 1000 kg/m³, so the mass of 0.9 m³ of water is 900 kg.
-- The weight of 900 kg of water is (mass) x (gravity)
= (900 kg) x (9.8 m/s²)
= 8,820 Newtons.
When the block is in water, it feels like it's that much LIGHTER, because that's the force of the water pushing UP on the block. It's the same reason why your big brother seems so light in the pool that you can pick him up and carry him.
So how heavy does this block FEEL in water ?
The force of gravity pulling down on it: 35,280 newtons The force of water pushing up on it: 8,820 newtons How heavy the block feels (the difference) 26,460 newtons
The question is written so poorly that even THIS number is not one of the choices.
Again, the thing to realize is that being in the water does NOT change the force of gravity on anything. It only creates another force, that acts against gravity.
Just like . . . When you walk up some stairs, how does it happen that you suddenly move upward, opposite to gravity. Does the force of gravity acting on you change ? No ! But you use your leg muscles to create another force in the opposite direction, that works against gravity, and makes you seem so light that you can actually move up, opposite to gravity.
Colors seen on the cover of our physics book result from color is due to Subtraction.
What is physics of color subtraction?
Some visible spectrum wavelengths are intentionally removed during the subtraction procedure.
For instance, the yellow filter transmits the green and red colors while blocking the blue.
Red and blue are transmitted while the green is blocked by the magenta filter.
Blue and green are transmitted while red is blocked by the cyan filter.
Subtractive mixing gets its name from the fact that when colors are mixed, wavelengths are removed from what we see because each paint absorbs some of the wavelengths that the other paint reflects, leaving us with less wavelengths afterward.
Learn more about Subtractive mixing with the help of the given link:
Inverse Square Law Newton proposed the Inverse Square Law. The effect of gravity (and also on forces such as sunlight) works like this. If say we have a half-mass Earth, it would produce a gravity of not half but a quarter (the square of 2).
The speed of the galaxy relative to the Earth is .
Explanation:
We have,
(a) Wavelength emitted by light at distant galaxy is 434.1 nm. On earth, the wavelength of this light is measured to be 438.6 nm. It can be seen that the wavelength of light reduces as it reaches Earth. It is called Red shift. As per Doppler's effect, we can say that the galaxy is receding from the Earth.
(b) Let v is the speed of the galaxy relative to the Earth. It can be given by :
So, the speed of the galaxy relative to the Earth is .
Molly could increase her heart rate by turning around and jogging backwards, by jogging on her hands instead of her feet, or by continuing to jog normally but increasing the speed of the treadmill.
