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4 years ago

6

Electromagnets can be used to lock doors. How could an engineer increase the strength of an electromagnetic lock? Check all that

apply
A. by increasing the current through the wire

B. by reversing the current through the electromagnet

C. by adding more coils to the electromagnet

D. by increasing the space between the coils in the electromagnet

1 answer:

ddd [48]4 years ago

3 0

The answer should be A

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kid shoots a BB gun directly upward at a ock of birds. The initial velocity of the BB is21 m/s. If the BB hits a bird at less th

Mademuasel [1]

Answer:

22.5 m

Explanation:

Using v² = u² - 2gy where u = initial velocity of BB = 21 m/s, v = final velocity of BB = 1 m/s (since this is the required speed of BB in which it will not harm the birds), g = acceleration due to gravity = 9.8 m/s² and y = minimum height of BB above the gun at which the birds may safely fly.

Substituting the values of the variables into the equation, we have

v² = u² - 2gy

(1 m/s)² = (21 m/s)² - 2(9.8 m/s²)y

collecting like terms, we have

(1 m/s)² - (21 m/s)² = - 2(9.8 m/s²)y

1 m²/s² - 441 m²/s² = -(19.6 m/s²)y

simplifying, we have

- 440 m²/s² = -(19.6 m/s²)y

dividing through by -19.6 m/s², we have

y = - 440 m²/s² ÷ -19.6 m/s²

y = 22.45 m

y ≅ 22.5 m

3 0

3 years ago

1. A huge spool of wire, 10,000 meters long, weighs 81.34 N. You cut off a meter or so and tie it between two posts, 0.660 m apa

WARRIOR [948]

Answer:

The beat frequency is 6.378 Hz.

Explanation:

Given that,

Length of wire = 10000 m

Weight = 81.34 N

Distance = 0.660 m

Tension = 52 N

Frequency = 196 Hz

We need to calculate the mass of the wire

Using formula of weight

$W= mg$

$m = \dfrac{W}{g}$

Put the value into the formula

$m=\dfrac{81.34}{9.8}$

$m=8.3\ kg$

The mass per unit length of the wire

$m_{l}=\dfrac{m}{l}$

Put the value into the formula

$m_{l}=\dfrac{8.3}{10000}$

$m_{l}=8.3\times10^{-4}\ kg/m$

We need to calculate the frequency in the wire

Using formula of frequency

$f_{w}=\dfrac{1}{2l}\sqrt{\dfrac{T}{m_{l}}}$

Put the value into the formula

$f_{w}=\dfrac{1}{2\times0.660 }\sqrt{\dfrac{52}{8.3\times10^{-4}}}$

$f_{w}=189.62\ Hz$

We need to calculate the beat frequency

Using formula of beat frequency

$f_{b}=f_{in}-f_{w}$

Put the value into the formula

$f_{b}=196-189.622$

$f_{b}=6.378\ Hz$

Hence, The beat frequency is 6.378 Hz.

5 0

3 years ago

Which force affect the movement of aeroplane and ship?

uranmaximum [27]

For aeroplane are lift,weight,thrust and drag
For ships are inertia,drag,buoyancy and gravity

7 0

4 years ago

A ball with mass 0.11 kg is thrown upward with initial velocity 10 m/s from the roof of a building 20 m high. Neglect air resist

inessss [21]

Answer:

a) $H=25.1020\ m$

b) $t=3.2838\ s$

Explanation:

Given:

mass of the ball thrown up, $m=0.11\ kg$

initial velocity of the ball thrown up, $u=10\ m.s^{-1}$

height above the ground from where the ball is thrown up, $h=20\ m$

a)

Maximum height attained by the ball above the roof level can be given by the equation of motion.

As,

$v^2=u^2-2g.h'$

where:

$v=$ final velocity at the top height of the upward motion $=0\ m.s^{-1}$

$g=$ acceleration due to gravity

$h'=$ height of the ball above the roof

Now,

$0^2=10^2-2\times 9.8\times h'$

$h'=5.10\ m$

Therefore total height above the ground:

$H=h+h'$

$H=20+5.1020$

$H=25.1020\ m$

b)

Now we find the time taken in raching the height $h'$ :

$v=u-gt'$

$v=$ final velocity at the top of the motion $=0\ m.s^{-1}$

So,

$0=10-9.8\times t'$

$t'=1.0204\ s$

Now the time taken in coming down to the ground from the top height:

$H=u'.t_d+\frac{1}{2} g.t_d^2$

where:

$u'=$ is the initial velocity of the ball in course of coming down to ground from the top $=0\ m.s^{-1}$

Here the direction acceleration due to gravity is same as that of motion so we are taking them positively.

$25.1020=0+0.5\times 9.8\times t_d^2$

$t_d=2.2634\ s$

Therefore the total time taken in by the ball to hit the ground after it begins its motion:

$t=t'+t_d$

$t=1.0204+2.2634$

$t=3.2838\ s$

4 0

3 years ago

What is the correct calculation for voltage if the resistance is 3 ohms and the current is 4 amps?

denis23 [38]

Answer:

iek

Explanation:

5 0

3 years ago