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4 years ago

Robby skateboards 0.50 blocks to his friend's house in 1.2 minutes. What is his speed?

Physics

2 answers:

KonstantinChe [14]4 years ago

5 0

.42 the direction of his friends house

bogdanovich [222]4 years ago

3 0

velocity = distance / time
v=0.50/1.2
v=0.42 blocks/min, in the direction of his friend's house
hope this helps

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You stand at the top of a deep well. To determine the depth, D, of the well you drop a rock from the top of the well and listen

Paladinen [302]

Answer:

(A)

$\displaystyle D^2-\left (\frac{2v_s^2}{g}+2t_tv_s \right )D+t_t^2v_s^2=0$

(B) D=54.71 m

Explanation:

Free Fall

When a particle is dropped in free air, it starts falling to the ground with an acceleration equal to the gravity. If one wanted to know the height of launching, it can indirectly be measured by the time it takes to reach the ground by the formula

$\displaystyle D=\frac{gt^2}{2}$

Solving for t

$\displaystyle t=\sqrt{\frac{2D}{g}}$

If we are taking into consideration the time we can hear the sound it makes when hitting the ground (or water in this case), we must also consider the speed of the sound for the time it takes to reach back our ears. That time can be computed from the basic equation for the speed

$\displaystyle t=\frac{D}{v_s}$

(A)

The total measured time is the sum of both times and it's given as $t_t=3.5\ seconds$

$\displaystyle t_t=\sqrt{\frac{2D}{g}}+\frac{D}{v_s}$

From this equation we'll manage to compute D

First, we isolate the square root

$\displaystyle \sqrt{\frac{2D}{g}}=t_t-\frac{D}{v_s}$

Let's square both sides

$\displaystyle \frac{2D}{g}=t_t^2-2t_t\frac{D}{v_s}+\frac{D^2}{v_s^2}$

Multiplying by $v_s^2$

$\displaystyle \frac{2Dv_s^2}{g}=t_t^2v_s^2-2t_tDv_s+D^2$

Rearranging and factoring

$\boxed{\displaystyle D^2-\left (\frac{2v_s^2}{g}+2t_tv_s\right )D+t_t^2v_s^2=0}$

Now, let's put in numbers:

$g=9.8\ m/s^2,\ v_s=345\ m/s,t_t=3.5\ sec$

$\displaystyle D^2-\left (\frac{2(345)^2}{9.8}+2(3.5)(345)\right )D+(12.25)345^2=0$

Computing all the coefficients:

$\displaystyle D^2-26,705.82D+1,458,056.25=0$

Solving for D, we have two possible solutions:

$D=54.71,\ D=26,651.11$

The second solution is called "extraneous", since it comes from squaring an equation, which can introduce non-valid (or external) solutions. It's impossible, given the conditions of the problem, that the well could be 26.5 km deep. So we'll keep the only solution as.

D=54.71 m

Let's prove our calculations by computing both times:

$\displaystyle t_1=\sqrt{\frac{2(54.71)}{9.8}}=3.34\ sec$

$\displaystyle t_2=\frac{54.71}{345}=0.16\ sec$

We can see their sum is 3.5 seconds, 3.34 of which were taken to reach the bottom of the well, and 0.16 sec took the sound to reach the top.

3 0

3 years ago

Physics // how i solve?

Alex

V=IR

180mA=V/R

I=2V/3R

I=2/3 x 180 mA =120 mA

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3 years ago

An object accelerating may be changing in what two ways

Oksana_A [137]

Velocity and direction

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3 years ago

Which wave causes the medium to vibrate only in a direction not parallel to the waves motion?

Paha777 [63]

The correct answer to the question is : Transverse wave.

EXPLANATION :

Before going to answer this question, first we have to understand the longitudinal and transverse wave.

LONGITUDINAL WAVE : A longitudinal wave is a mechanical wave in which the direction of vibration of particles is parallel to the direction of wave propagation. It moves in the form of compression and rarefaction.

For instance, sound wave.

TRANSVERSE WAVE : A transverse wave is a mechanical wave in which the direction of vibration of particles is perpendicular to the direction of wave propagation. It moves in the form of crests and troughs.

For instance, the wave created in a pond when a stone is dropped into it.

Hence, the correct answer of this question is transverse wave.

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