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wolverine [178]
3 years ago
11

You and your friend Peter are putting new shingles on a roof pitched at 20°. You're sitting on the very top of the roof when Pet

er, who is on the edge of the roof, 5.1 m away, asks you for the box of nails. Rather than carry the 2.2 kg box of nails down to Peter, you decide to give the box a push and have it slide down to him.
If the coefficient of kinetic friction between the box and the roof is 0.53, with what speed should you push the box to have it gently come to rest right at the edge of the roof?
Physics
1 answer:
dexar [7]3 years ago
6 0

Answer:

vi = 3.95 m/s

Explanation:

We can apply the Work-Energy Theorem as follows:

W = ΔE = Ef - Ei

W = - Ff*d

then

Ef - Ei = - Ff*d   <em> </em>

If

Ei = Ki + Ui = 0.5*m*vi² + m*g*hi = 0.5*m*vi² + m*g*hi = m*(0.5*vi² + g*hi)

hi = d*Sin 20º = 5.1 m * Sin 20º = 1.7443 m

Ef = Kf + Uf = 0 + 0 = 0

As we know,   vf = 0  ⇒ Kf = 0

Uf = 0  since hf = 0

we get

W = ΔE = Ef - Ei = 0 - m*(0.5*vi² + g*hi)  ⇒   W = - m*(0.5*vi² + g*hi)   <em> (I)</em>

<em />

If

W = - Ff*d = - μ*N*d = - μ*(m*g*Cos 20º)*d = -  μ*m*g*Cos 20º*d    <em>(II)</em>

<em />

we can say that

<em />

- m*(0.5*vi² + g*hi) = -  μ*m*g*Cos 20º*d  

⇒ vi = √(2*g*(μ*Cos 20º*d - hi))  

⇒ vi = √(2*(9.81 m/s2)*(0.53*Cos 20º*5.1m - 1.7443 m)) = 3.95 m/s

<em />

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The bigclaw snapping shrimp shown in (Figure 1) is aptly named--it has one big claw that snaps shut with remarkable speed. The p
leva [86]

1) 1.86\cdot 10^6 rad/s^2

2) 2418 rad/s

3) 27000 m/s^2

4) 36.3 m/s

Explanation:

1)

The angular acceleration of an object in rotation is the rate of change of angular velocity.

It can be calculated using the following suvat equation for angular motion:

\theta=\omega_i t +\frac{1}{2}\alpha t^2

where:

\theta is the angular displacement

\omega_i is the initial angular velocity

t is the time

\alpha is the angular acceleration

In this problem we have:

\theta=90^{\circ} = \frac{\pi}{2}rad is the angular displacement

t = 1.3 ms = 0.0013 s is the time elapsed

\omega_i = 0 is the initial angular velocity

Solving for \alpha, we find:

\alpha = \frac{2(\theta-\omega_i t)}{t^2}=\frac{2(\pi/2)-0}{0.0013}=1.86\cdot 10^6 rad/s^2

2)

For an object in accelerated rotational motion, the final angular speed can be found by using another suvat equation:

\omega_f = \omega_i + \alpha t

where

\omega_i is the initial angular velocity

t is the time

\alpha is the angular acceleration

In this problem we have:

t = 1.3 ms = 0.0013 s is the time elapsed

\omega_i = 0 is the initial angular velocity

\alpha = 1.86\cdot 10^6 rad/s is the angular acceleration

Therefore, the final angular speed is:

\omega_f = 0 + (1.86\cdot 10^6)(0.0013)=2418 rad/s

3)

The tangential acceleration is related to the angular acceleration by the following formula:

a_t = \alpha r

where

a_t is the tangential acceleration

\alpha is the angular acceleration

r is the distance of the point from the centre of rotation

Here we want to find the tangential acceleration of the tip of the claw, so:

\alpha = 1.86\cdot 10^6 rad/s is the angular acceleration

r = 1.5 cm = 0.015 m is the distance of the tip of the claw from the axis of rotation

Substituting,

a_t=(1.86\cdot 10^6)(0.015)=27900 m/s^2

4)

Since the tip of the claw is moving by uniformly accelerated motion, we can find its final speed using the suvat equation:

v=u+at

where

u is the initial linear speed

a is the tangential acceleration

t is the time elapsed

Here we have:

a=27900 m/s^2 (tangential acceleration)

u = 0 m/s (it starts from rest)

t = 1.3 ms = 0.0013 s is the time elapsed

Substituting,

v=0+(27900)(0.0013)=36.3 m/s

5 0
3 years ago
HEYYYY!! PLEASE HELP!!! Describe three machines that humans have designed and explain how the mechanical advantage is used.!!
satela [25.4K]

Answer:

Three machines that humans have created are the lever, the wheel, and the axle, and also a pulley. even though there's actually more. A lever is A rigid bar that is free to move around a fixed point, such as a screwdriver. The wheel and axle, everyone should know what that is and what it does, it lifts heavy objects, moves people quickly, and moves parts of a complex machine. Pulleys are used to lift things, pulleys can be used singly or with many pulleys working together in order to transport people or things. They can also be used to provide power from one shaft to another. ... Construction pulleys are used in order to lift and place heavy materials.

5 0
3 years ago
At baseball practice, Mason and Alfredo both picked up the same bat and neither would let go until one of them had it for himsel
Illusion [34]

Answer:

Option B. O because the net force was 5 N in Alfredo's direction

Explanation:

To know the the correct answer to the question given above, we shall determine the net force acting on the bat. This can be obtained as follow:

Force of pull by Mason (Fₘ) = 15 N

Force of pull by Alfredo (Fₐ) = 20 N

Net force (Fₙ) =?

Fₙ = 20 – 15

Fₙ = 5 N in Alfredo's direction

From the calculation made above, we can see that the net force is 5N in Alfredo's direction. This is the reason why Alfredo end up having the bat.

7 0
3 years ago
A car drives around a curve with a radius of 42 m at a velocity of 24 m/s. What is the centripetal acceleration of the car?
defon
Hope this helps you.

8 0
3 years ago
Read 2 more answers
What is the speed of an 800 kg automobile if it has a kinetic energy of 9.00 x 10^J?
MA_775_DIABLO [31]

Ek = 1/2 mv^2

9 × 10^4 = 1/2 × 800 × v^2

9 × 10^4/400 = 400 v^2 / 400

9 × 10^4/400 = v^2

√225 = v

15 ms⁻¹ = v

That's the only way I know how to work it out

I think in this case velocity and speed would be considered the same because me

s = d/t and v=d/t

one is distance travelled and the other is displacement of a body

7 0
2 years ago
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