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4 years ago

If an exit sign is hanging from the ceiling by three chains each of which has a tension of 15N what is the weight of the sign

1 answer:

3 0

The weight is 45 N, because the three chains hold the sign, and each contributes 15 N.

Notice that the mass would be the weight/acceleration of gravity, m = 45/9.8 kg. But they ask the weight (force, so Newtons)

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A ductile metal wire has resistance R. What will be the resistance of this wire in terms of R if it is stretched to three times

Ira Lisetskai [31]

Answer:

Explanation:

We know that the resistance is $R=\rho *\frac{L}{A}$ .

If we stretch the wire to a new length L2 = 3L, the cross-sectional area will also change. If the cross-sectional area doesn't change throughout the wire, we can say that:

Volume = L*A = 3L * A2 being A2 the new area after stretching the wire.

Since the volume remains the same we conclude that A2 = A/3

With this information, we calculate the new resistance:

$R2=\rho *\frac{L2}{A2}=\rho *\frac{3*L}{A/3}=\rho * 9 * \frac{L}{A}$

Since $R=\rho *\frac{L}{A}$ , and by simple inspection of the previous equation, we get:

6 0

3 years ago

A general contractor drives 5 miles to the hardware store in 10 minutes. He shops for needed tools for 30 minutes, then drives t

Alex17521 [72]

Given parameters:

Distance to hardware shop = 5 miles

Time to reach hardware shop = 10 minutes

Time spent at the shop = 30 minutes

Average speed to customer home = 45 mph

Time taken for the travel = 20 minutes

Unknown:

Average speed of the contractor = ?

Solution:

Average speed is the total distance covered divided by the total time taken.

Average speed = $\frac{total distance}{total time taken}$

total distance = distance to hardware shop + distance to customer's home

We do not know the distance to customer's home but we have been given the speed and time, so we can find the distance.

Distance = speed x time

Convert the time to hrs and solve;

60 minutes = 1 hr

20 minutes = $\frac{20}{60} hr$ = $\frac{1}{3} hr$

So, Distance = 45mph x $\frac{1}{3} hr$ = 15miles

Now;

Total distance = 5 + 15 = 20miles

Total time = time to reach hardware shop + time to reach customer's house

= 10 + 20

= 30 minutes

Convert the time from minutes to hrs;

60 minutes = 1hr

30 minutes = $\frac{30}{60}$ = 0.5hr

So;

Average speed = $\frac{20}{0.5}$ = 40mph

The average speed is 40mph

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4 years ago

Which statement about the atomic nucleus is correct? a. The nucleus is made of protons and neutrons and has a negative charge. b

Anon25 [30]

"b. The nucleus is made of protons and neutrons and has a positive charge" is the only option that is true about the atomic nucleus. The protons give it a positive charge.

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4 years ago

5. Granny Goodwitch boards a bus at the local shopping center. The bus travels an

irina [24]

As BBC ztrrtv B 4 C w.a)z

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3 years ago

In which situation is work not being done?

almond37 [142]

work done =W = F.d = F d cosФ (Ф is angle between force F and displacement d) If a body/object is moving on a smooth surface (friction-less surface ) .There is no force acting on that body. F=0 so W=FdcosФ= (0)dcosФ ⇒ W=0

Now if a body is facing some amount of force but under the action of force there is no displacement covered. d=0 so W =FdcosФ= F(0)cosФ ⇒W=0

example: A person is applying a force on rigid wall but wall remains at rest there is no displacement occurs in wall.

The third term upon which work done dependent is angle between force and displacement i.e Ф. If Ф=90° then W= FdcosФ= Fdcos90⇒ W=0 ( as cos 90°=0)

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3 years ago