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2 years ago

A train travels 81 kilometers in 2 hours and then 90 kilometers in two hours. wat is the average speed

1 answer:

5 0

I'm assuming your question refers to the train travels 81 km in 2 hours, as in that's the total distance covered versus the speed for those 2 hours, whereas the 90 km in 2 hours the second time around is the total distance not speed I would assume.

Now... if it was going 81 km for the first 2 hours and 90 km for the second 2 hours then the average speed would be the mean of these numbers, with that being 85.5 km. Though, I doubt that's your question.

With that said, 81 km covered by 2 hours and 90 km covered by 2 more hours. To acquire the km an hour average, we'll have to divide the distance by how many hours it traveled:
81 / 2 = 40.5
90 / 2 = 45

Meaning the train was going 40.5 km an hour for the first 2 hours and 45 km an hour for the second 2 hours. Now, to find the mean:
40.5 + 45 = 85.5 / 2 = 42.75

In-case you were wondering, the mean is the sum of all the numbers in a set, divided by the total amount of numbers in that set, take for instance:
3, 5, 9, 2, 1, 5. -> There are 6 numbers in this set.
3 + 5 + 9 + 2 + 1 + 5 = 25 -> 25 is the sum of these numbers.
25 / 6 = 4.2 (estimated) -> 4.2 is roughly the mean or average between the original set.

Anyhow, with that aside the average speed between this I would believe would be 42.75 km an hour. I hope that helps, have a great rest of your day! ^ ^
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When you stretch a spring 20 cm past its natural length, it exerts a force of 8

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Answer:

40 N/m

Explanation:

F = -kx (This is the Hooke's Law equation)

F is the force the spring exerts = 8 N

-k = spring constant

x = displacement (The distance stretched past it's natural length) = 20cm

x needs to be in meters, and 20 cm is = to 0.2 meters

Finally:

8N = -k (0.2m)

-k = 8N / 0.2 m

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2 years ago

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Glycerin is poured into an open U-shaped tube until the height in both sides is 20 cm. Ethyl alcohol is then poured into one arm

lina2011 [118]

Answer:

Difference in height = 7.5 cm

Explanation:

We are given;.

Height of ethyl alcohol;h2 = 20 cm = 0.2 m

Density of glycerin: ρ1 = 1260 kg/m³

Density of ethyl alcohol; ρ2 = 790 kg/m³

To get the difference in height, the pressure at the top of the open end must be equal to the pressure at the point where the liquids do not mix since both points will be at different levels after the pouring.

Thus;

P1 = P2

Formula for pressure is; P = ρgh

Thus;

ρ1 × g × h1 = ρ2 × g × h2

g will cancel out to give;

ρ1 × h1 = ρ2× h2

Making h1 the subject, we have;

h1 = (ρ2× h2)/ρ1

h1 = (790 × 0.2)/1260

h1 = 0.125 m

Difference in height will be;

Δh = h2 - h1

Δh = 0.2 - 0.125

Δh = 0.075 m = 7.5 cm

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2 years ago

Convert 1erg into joule by dimensional method

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Answer:

1 * 10^-7 [J]

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A boat of mass 250 kg is coasting, with its engine in neutral, through the water at speed 1.00 m/s when it starts to rain with i

Vera_Pavlovna [14]

Answer:

Explanation:

1. We use the conservation of momentum for before the raining and after. And also we take into account that in 0.5h the accumulated water is

100kg/h*0.5h = 50kg

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2. the momentum does not conserve because the drag force of water makes that the boat loses velocity

3. If we assume that the force of the boat before the raining is

$F=ma=m\frac{v-v_{0}}{t-t_{0}}=250kg\frac{1m}{s^{2}}=250N$

where we have assumed that the acceleration of the boat is 1m/s{2} just before the rain starts

And if we take the net force as

$F_{net}=M_{b}a_{net}=F-F_{d}=250N-bv^{2}\\F_{net}=250N-0.5N\frac{s^{2}}{m^{2}}(1\frac{m}{s})^{2}=249.5N\\a_{net}=\frac{249.5N}{M_{b}}=\frac{249.5N}{250kg}=0.99\frac{m}{s^{2}}$

where we take v=1m/s because we are taking into account tha velocity just after the rain stars.

I hope this is useful for you

regards

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3 years ago