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2 years ago

What is Marie's instantaneous speed at 20 minutes in miles/min?

Physics

1 answer:

AVprozaik [17]2 years ago

8 0

Answer:

0.25miles/min

Explanation:

Instantaneous speed of a person or an object is its speed at a particular moment usually at a period of time.

The speedometer of a car reports the instantaneous speed.

It can be mathematically expressed as;

Instantaneous speed = $\frac{distance}{time}$

At 20min the distance covered is 5miles;

Instantaneous speed = $\frac{5 miles }{20mins}$ = 0.25miles/min

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Two ice skaters, Daniel (mass 70.0 kg) and Rebecca (mass 45.0 kg), are practicing. Daniel stops to tie his shoelace and, while a

wel

Answer:

a) $v=7.32m/s$

b) $\alpha =-35$ º

c) $ΔK=-1094.62J$

Explanation:

From the exercise we know that the collision between Daniel and Rebecca is elastic which means they do not stick together

So, If we analyze the collision we got

$p_{1x}=p_{2x}$

To simplify the problem, lets name D for Daniel and R for Rebecca

a) $p_{D1x}+p_{R1x}=p_{D2x}+p_{R2x}$

Since Daniel's initial velocity is 0

$m_{R}v_{Rx}=m_{D}v_{D2x}+m_{R}v_{R2x}$

$v_{D2x}=\frac{m_{R}*v_{R1x}-m_{R}*v_{R2x}}{m_{D}}$

$v_{D2x}=\frac{(45kg)(14m/s)-(45kg)(8cos(55.1)m/s)}{(70kg)}=6m/s$

Now, lets analyze the movement in the vertical direction

$p_{1y}=p_{2y}$

Since $p_{1y}=0$

$0=m_{D}v_{D2y}+m_{R}v_{R2y}$

$v_{D2y}=-\frac{m_{R}v_{2Ry}}{m_{D}}=-\frac{(45kg)(8sin(55.1)m/s)}{(70kg)}=-4.21m/s$

Now, we can find the magnitude of Daniel's velocity after de collision

$v_{D}=\sqrt{(6m/s)^2+(-4.21m/s)^2}=7.32m/s$

b) To know whats the direction of Daniel's velocity we need to solve the arctan of the angle

$\alpha =tan^{-1}(\frac{v_{y}}{v_{x}})=tan^{-1}(\frac{-4.21}{6})=-35$ º

c) The change in the total kinetic energy is:

ΔK= $K_{2}-K_{1}$

ΔK= $\frac{1}{2}[(45kg)(8m/s)^2+(70kg)(7.32m/s)^2-(45kg)(14m/s)^2]=-1094.62J$

That means that the kinetic energy decreases

5 0

2 years ago

A piece of wire 25 m long is cut into two pieces. One piece is bent into a square and the other is bent into an equilateral tria

Dmitry [639]

Answer:

10.87 m

Explanation:

Total length of the wire = 25 m

Let the length of one piece is y and other piece is 25 - y

Let the side of square is a.

So, 4 a = y

a = y / 4

And the side of triangle is b

3 b = (25 - y)

b = (25 - y) / 3

Area of square, A1 = side x side =

A1 = y² / 16

Area of equilateral triangle, A2 = $\frac{\sqrt{3}}{4}\times b^{2}$

$A_{2}=\frac{\sqrt{3}}{4}\frac{\left ( 25-y \right )^{2}}{9}$

Total area, A = A1 + A2

$A=\frac{y^{2}}{16}+\frac{\sqrt{3}}{4}\frac{\left ( 25-y \right )^{2}}{9}$

For maxima and minima, fins dA /dy

$\frac{dA}{dy}=\frac{y}{8}-\frac{1.732}{18} \times \frac{25-y}{1}$

It is equal to zero.

$\frac{y}{8}=\frac{1.732}{18} \times \frac{25-y}{1}$

9y = 173.2 -6.928 y

15.928 y = 173.2

y = 10.87 m

So, the length of wire to make square is 10.87 m.

3 0

3 years ago

A football is thrown at an angle of 44◦ above the horizontal. Assume the ball is throw and received at the same height. To throw

aleksley [76]

Answer:

The initial speed of the ball is 23.3 m/s.

Explanation:

Given that,

Angle = 44°

Range = 55.7 m

We need to calculate the initial speed of the ball

Using formula of range

$R=\dfrac{u^2\sin2\theta}{g}$

Where. u = initial velocity

r = range

g = acceleration due to gravity

Put the value into the formula

$55.7=\dfrac{u^2\sin2\times44}{9.8}$

$u^2=\dfrac{55.7\times9.8}{\sin88}$

$u=\sqrt{\dfrac{55.7\times9.8}{\sin88}}$

$u=23.3\ m/s$

Hence, The initial speed of the ball is 23.3 m/s.

4 0

2 years ago

If a person weighs 717 N on earth and 5320 N on the surface due to gravity on that planet? of a nearby planet, what is the accel

Studentka2010 [4]

The answer is B. You divide 717 by the acceleration by gravity of earth (9.8 m/s) and divide 5320 by your answer.

4 0

3 years ago

Read 2 more answers

If someone drops a cup it falls to the ground why doesn’t the gravationalbforce between the persons hand and the cup keep the cu

insens350 [35]

Answer:

There is a gravitational force between the hand and the cup, but Earth's gravity is stronger, so Earth's gravity pulls the cup down.

6 0

3 years ago