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4 years ago

While skateboarding at 19 km/h throwning a tennis ball at 11 km/h what is the speed of the ball

Physics

1 answer:

Lina20 [59]4 years ago

3 0

According to whom ?

So YOU're on your skateboard, and there's somebody else, sitting on HIS porch, watching you skate by on your board.

-- The man on the porch says you're skating by him at 19 km/hr .

-- You throw a tennis ball.

. . . . . Do you throw it in the same direction that you're skateboarding, or do you throw it away behind you, toward the place you just came from ?

. . . . . Does it fly away from YOU at 11 km/hr ? Or does it fly past the man on the porch at 11 km/hr ?

There are 4 possible combinations. One of them is not possible. Each of the other three combinations leads to two different answers to the question. And ALL six answers are correct !

1). You throw the ball forward, in the same direction you're skating. It flies away from your hand at 11 km/hr.

To you, the speed of the ball is 11 km/hr, in the direction you're skating. To the man on the porch, it's 30 km/hr, in the direction you're skating.

2). You throw the ball forward, in the same direction you're skating. It flies past the porch at 11 km/hr.

This isn't possible.

3). You throw the ball backward, toward where you just came from. It flies away from YOU at 11 km/hr.

To you, the speed of the ball is 11 km/hr, in the direction backward from you. To the man on the porch, the speed of the ball is 10 km/hr in the direction you're skating.

4). You throw the ball backward, toward where you just came from. It flies past the porch at 11 km/hr.

To you, the speed of the ball is 8 km/hr, in the direction backward from you. To the man on the porch, it's 11 km/hr in the direction you're skating.

NOW you're going to ask me "But what's the REAL speed of the ball ?"

The answer to THAT one is: There's no such thing ! It all depends on WHO's measuring it ... where that observer is and how HE's moving.

The displacement, speed, velocity, acceleration, and energy of the ball, ALL depend on who's watching it and measuring it.

I'll be interested to see whether you mark this answer 'Brainliest', or report it because it's weird, confusing, and ridiculous.

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A 80 kg skier grips a moving rope that is powered by an engine and is pulled at constant speed to the top of a 25 degrees hill.

zloy xaker [14]

Answer:

$P=28.085\,hp$

Explanation:

Given that:

mass of 1 skier, $m=80kg$

inclination of hill, $\theta=25^{\circ}$

length of inclined slope, $l=220m$

time taken to reach the top of hill, $t=2.3 min= 138 s$

coefficient of friction, $\mu=0.15$

Now, force normal to the inclined plane:

$F_N=m.g.cos\theta$

$F_N=80\times 9.8\times cos25^{\circ}$

$F_N=710.54\,N$

Frictional force:

$f=\mu.F_N$

$f=0.15\times 710.54$

$f=106.58\,N$

The component of weight along the inclined plane:

$W_l=m.g.sin\theta$

$W_l=80\times 9.8\times sin25^{\circ}$

$W_l=331.33\,N$

Now the total force required along the inclination to move at the top of hill:

$F=f+W_l$

$F=106.58+331.33$

$F=437.91\,N$

Hence the work done:

$W=F.l$

$W=437.91\times 220$

$W=96340.80\,J$

Now power:

$P=\frac{W}{t}$

$P=\frac{96340.80}{138}$

$P=698.12\,W$

So, power required for 30 such bodies:

$P=30\times 698.12$

$P=20943.65\,W$

$P=\frac{20943.65}{745.7}$

$P=28.085\,hp$

8 0

3 years ago

Iron filings were sprinkled around these two magnets. What do the iron filings

Sever21 [200]

Answer:

B. They show the pattern made by the magnetic field lines around the

magnets

Explanation:

Using iron fillings, the pattern of the magnetic field lines around a bar magnet can be known.

Magnetic field lines are the line of force around a bar magnet.

These iron fillings will trace the pattern of the magnetic field around the magnet.
The domains of the iron fillings begins to align and orient with that of the prevailing magnetic field around.
Those areas with the strongest force will attract more fillings and those far away will attract lesser fillings.

3 0

3 years ago

Read 2 more answers

(a) You short-circuit a 20 volt battery by connecting a short wire from one end of the battery to the other end. If the current

erica [24]

(a) $1.11 \Omega$

When the battery is short-cut, the only resistance in the circuit is the internal resistance of the battery. Therefore, we can apply Ohm's law:

$r=\frac{V}{I}$

where

V = 20 V is the voltage across the internal resistance of the battery

I = 18 A is the current flowing through it

Solving the equation,

$r=\frac{20 V}{18 A}=1.11\Omega$

(b) 360 W

The power generated by the battery is given by the equation

$P=VI$

where

V = 20 V is the voltage of the battery

I = 18 A is the current

Substituting into the formula,

$P=(20 V)(18 A)=360 W$

(c) 360 J

The energy dissipated by the internal resistance is given by

$E=Pt$

where

P = 360 W is the power generated

t = 1 s is the time

Solving the equation, we find

$E=(360 W)(1 s)=360 J$

(d) 1.65 A

The battery is now connected to a $R=11 \Omega$ resistor. This means that the internal resistance of the battery is now connected in series with the other resistor R: so, the total resistance of the circuit is

$R_T = r+R=1.11 \Omega +11 \Omega = 12.11 \Omega$

And so, the current flowing through the circuit is

$I=\frac{V}{R_T}=\frac{20 V}{12.11\Omega}=1.65 A$

(e) 29.9 W

The power dissipated in the external resistor is given by

$P=I^2 R$

where

I = 1.65 A is the current

$R=11 \Omega$ is the resistance

Solving the equation, we find

$P=(1.65 A)^2(11 \Omega)=29.9 W$

(f) 18.17 V

The terminals of the voltmeter are placed at the two end of the battery. The battery provides an emf of 20 V, however due to the internal resistance, some of this voltage is dropped across the internal resistance. Therefore, the actual potential difference that will be read by the voltmeter will be:

$V=\epsilon - Ir =20 V -(1.65 A)(1.11 \Omega)=18.17 V$

4 0

3 years ago

Supply the missing force necessary to achieve equilibrium. Show your work.

Mumz [18]

Analysing the Question:

We know that equilibrium is the state of a body when it has equal and opposite forces being applied on it

In this case, a net downward force of 496N is being applied and a net upward force of (106 + 106 + 142 + x) N

Finding the missing force:

Since we have to achieve equilibrium, the net upward forces have to be equal to the net downward forces

So, (106 + 106 + 142 + x) = 496

354 + x = 496

x = 496 - 354

x = 142 N

Therefore, the missing force is 142 N

8 0

3 years ago

The physics of wind instruments is based on the concept of standing waves. When the player blows into the mouthpiece, the column

JulsSmile [24]

Answer:

1) f = 214 Hz , 2) answer is c , 3) f = 428 Hz , 4) f₂ = 428 Hz , f₃ = 643Hz

Explanation:

1) A tube with both ends open, the standing wave has a maximum amplitude and a node in its center, therefore

L = λ / 2

λ = 2L

λ = 2 0.8

λ = 1.6 m

wavelength and frequency are related to the speed of sound (v = 343 m / s)

v =λ f

f = v / λ

f = 343 / 1.6

f = 214 Hz

2) In this case the air comes out through the open hole, so we can assume that the length of the tube is reduced

λ' = 2 L ’

as L ’<L₀

λ' <λ₀

f = v / λ'

f' > fo

the correct answer is c

3) in this case the length is L = 0.40 m

λ = 2 0.4 = 0.8 m

f = 343 / 0.8

f = 428 Hz

4) the different harmonics are described by the expression

λ = 2L / n n = 1, 2, 3

λ₂ = L

f₂ = 343 / 0.8

f₂ = 428 Hz

λ₃ = 2 0.8 / 3

λ₃ = 0.533 m

f₃ = 343 / 0.533

f₃ = 643 Hz

4,1) as we have two maximums at the ends, all integer multiples are present

the answer is C

E) the length of an open pipe created that has a wavelength of lam = 1.6 m is requested

in this pipe there is a maximum in the open part and a node in the closed part, so the expression

L = λ / 4

L = 1.6 / 4

L = 0.4 m

the answer is C

F) in this type of pipe the general expression is

λ = 4L / n n = 1, 3, 5 (2n + 1)

therefore only odd values can produce standing waves

λ₃ = 4L / 3

λ₃ = 4 0.4 / 3

λ₃ = 0.533

f₃ = 343 / 0.533

f₃ = 643 Hz

5 0

3 years ago