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3 years ago

Why are the action and reaction forces described by Newton’s third law of motion excluded in the free-body diagram of an object?

Physics

2 answers:

Lorico [155]3 years ago

6 0

The correct answer is:

B. They act on different objects, so they would not appear together.

Let's take for example a box sitting on a table. If we draw the free-body diagram of the box, we would draw two forces:

- the weight of the box (downward)

- the normal reaction of the table on the box (upward)

However, this is not a pair of action-reaction forces as described in Newton's third law. In fact, the correct action-reaction pair would be:

- weight of the box (=gravitational force exerted by the Earth on the box)

- gravitational force exerted by the box on the Earth

We see that these two forces act on two different objects (the first one on the box, the second one on the Earth), so they do not appear in the same free-body diagram.

umka2103 [35]3 years ago

4 0

B. They act on different objects, so they would not appear together.

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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

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3 years ago

A car travels 40 miles in 30 minutes.

lukranit [14]

Answer:

(a)Average velocity ,v =128.74 Km/hr

(b)Kinetic Energy , K=958546.875 Joule

(c)Distance, s=268.8m

(d)Acceleration, a= - 2.38 $m/s^2$

Explanation:

Given:

Distance travelled = 40 miles

Time taken = 30 minutes.

(A) The average velocity in kilometres/hour

Converting 40 miles into km ,

we know that,

1 mile = 1.60934

40 miles = 40 x 1.60934

so 40 miles = 64.3738 Km

similarly converting 30 minutes into hours

1 minute = $\frac{1}{60}hours$

30 minute = $\frac{30}{60}hours$

30 minute = $\frac{1}{2}hours$

Now

Average velocity = $\frac{Speed}{time}$

Substituting Values,

Average velocity = $\frac{64.3738}{\frac[1}{2}}$

Average velocity = $64.3738 \times 2$

Average velocity =128.74 Km/hr

(B) If the car weighs 1.5 tons, what is its If the car weighs 1.5 tons, what is its kinetic energy in joules (Note: you will need to convert your velocity to m/s)? in joules (Note: you will need to convert your velocity to m/s)?

Converting 1.5 tons into kg we get

1 ton = 1000 kg

so 1.5 ton =1500 kg

converting velocity to m/s

$128.74 \times \frac{5}{18}$