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2 years ago

7

A girl, standing on a bridge, throws a stone vertically downward with an initial velocity of 12.0 m/s, into the river below. if

the stone hits the water 2.50 seconds later, what is the height of the bridge above the water?

1 answer:

erica [24]2 years ago

3 0

Answer:

60.7 m high

Explanation:

d = v t + 1/2 a t^2

= 12 (2.5) + 1/2 (9.81)(2.5^2) = 60.7 m

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A particle travels along a straight line with a velocity v = (12 - 3t) m/s, where t is in seconds. When t = 1 s, the particle is

Simora [160]

Answer:

(1).The acceleration is -24 m/s²

The total distance is 912 m.

(2). The distance traveled before it stop is 78 m.

Explanation:

Given that,

Velocity = (12-3t^2) m/s

When t = 1 s, the particle is located 10 m to the left of the origin.

We need to calculate the acceleration at t = 4 sec

Using formula of acceleration

$a=\dfrac{dv}{dt}$

Put the value of v

$a=\dfrac{d}{dt}(12-3t^2)$

$a=-6t$

Put the value of t

$a=-6\times4$

$a=-24\ m/s^2$

The displacement from t = 0,t = 10 s, and the distance the particle travels during this time period.

We need to calculate the distance

Using formula of distance

$ds=v\ dt$

$\int_{-10}^{s}=\int_{1}^{t}{v}dt$

Put the value of v

$\int_{-10}^{s}=\int_{1}^{t}{ (12-3t^2)}dt$

$s+10=12t-t^3-11$

$s=12t-t^3-21$

At t = 0,

$s_{t=0}=-21$

At t = 10,

$s_{t=10}=12\times10-10^3-21$

$s_{t=10}=-901$

The displacement is

$\Delta s=-901-(-21)$

$\Delta s=-880\ m$

The distance at t= 2 sec

$s_{t=2}=12\times2-2^3-21$

$s_{t=2}=-5$

The total distance will be,

$s_{T}=(21-5)+(901-5)$

$s_{T}=912\ m$

(2). We need to calculate the distance at 2 sec

Using equation of motion

$s=ut-\dfrac{1}{2}at^2$

Put the value into the formula

$s=27\times 2+\dfrac{1}{2}\times6\times(2)^3$

$s=78\ m$

Hence, (1).The acceleration is -24 m/s²

The total distance is 912 m.

(2). The distance traveled before it stop is 78 m.

3 0

3 years ago

A wave with a frequency of 840 cycles per second has what period? Please help me !!

sweet-ann [11.9K]

Answer:

0.005556

Explanation:

The period of a typical class at a high school might be 55 minutes; every 55 minutes a class cycle begins (50 minutes for class and 5 minutes for passing time means that a class begins every 55 minutes). The period for the minute hand on a clock is 3600 seconds (60 minutes); it takes the minute hand 3600 seconds to complete one cycle around the clock.

<u>How to get period from frequency</u>

The formula for the period is T = 1 / f, where "T" is period – the time it takes for one cycle to complete, and "f" is frequency.
To get period from frequency, first convert frequency from Hertz to 1/s.
Now divide 1 by the frequency. The result will be time (period) expressed in seconds.

7 0

3 years ago

A father racing his son has half the kinetic energy of the son, who has half the mass of the father.The father speeds up by 1.0

Helga [31]

Answer:

(a) $v_f=2.414\ m.s^{-1}$

(b) $v_s=4.828\ m.s^{-1}$

Explanation:

Let:

mass of father be, $m_f$

mass of son be, $m_s=\frac{m_f}{2}$

speed of son be, $v_s$

initial speed of father be, $v_f$

After speeding up, speed of father is $v_f+1$

<u>We know Kinetic Energy is given as</u>

$KE=\frac{1}{2} m.v^2$ .....................................(1)

where:

m = mass

v = velocity

Hence, according to the initial condition the father is having kinetic energy half the kinetic energy of the son.

$KE_s=2.KE_f$

$\frac{1}{2} m_s.v_s^2=2\times \frac{1}{2} m_f.v_f^2$

$(\frac{m_f}{2})\times v_s^2=2\times m_f\times v_f^2$

$v_s=2v_f$ .................................................(2)

According to the final condition:

$\frac{1}{2} m_s.v_s^2= \frac{1}{2} m_f.(v_f+1)^2$

$(\frac{m_f}{2})\times v_s^2=m_f.(v_f+1)^2$

$v_s^2=2(v_f+1)^2$

$v_s=\sqrt{2}(v_f+1)$ .....................................................(3)

(a)

From eq. 2 & 3

$2v_f=\sqrt{2}(v_f+1)$

$\sqrt{2}\ v_f=(v_f+1)$

$v_f(\sqrt{2}-1)=1$

$v_f=\frac{1}{(\sqrt{2}-1)}$

$v_f=2.414\ m.s^{-1}$

(b)

<em>putting the above value in eq. (2)</em>

$v_s=4.828\ m.s^{-1}$

4 0

4 years ago

A car advertisement claims their car can go from a stopped position to 60 miles per hour in 5 seconds. The advertisement is desc

Komok [63]

Answer:

Acceleration

Explanation:

The advertisement is describing the acceleration of the car.

Acceleration is the rate of change of velocity per unit of time. It can be expressed mathematically as;

Acceleration = $\frac{v - u}{t}$

v is the final velocity

u is the initial velocity

t is the time taken

Any quantity that specifies the rate of change of velocity of a body within a given time frame is describing its acceleration.

5 0

3 years ago

A springboard diver intending to do a somersault brings her knees and arms closer to her body during the dive. What effect does

Hoochie [10]

During the diving when a diver jumps off from platform he brings her knees and arms closer to the body

This is because when diver is in air he don't have any torque about his center of mass which shows that angular momentum of his body will remain constant during his motion in air

Now we can say product of his moment of inertia and his angular speed will remain constant always

So here if we decrease the moment of inertia of the body during our motion then angular speed will increase so that product will remain constant

and this is what the diver use during his diving

so correct answer will be

<u><em>It decreases her moment of inertia.</em></u>

7 0

4 years ago