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3 years ago

11

Why are objects that fall near earth’s surface rarely in free fall?

1 answer:

Sloan [31]3 years ago

3 0

Answer:

Because of the presence of air resistance

Explanation:

When an object is in free fall, ideally there is only one force acting on it:

- The force of gravity, W = mg, that pushes the object downward (m= mass of the object, g = acceleration of gravity)

However, this is true only in absence of air (so, in a vacuum). When air is present, it exerts a frictional force on the object (called air resistance) with upward direction (opposite to the motion of free fall) and whose magnitude is proportional to the speed of the object.

Therefore, it turns out that as the object falls, its speed increases, and therefore the air resistance acting against it increases too; as a result, the at some point the air resistance becomes equal (in magnitude) to the force of gravity: when this happens, the net acceleration of the object becomes zero, and so the speed of the object does not increase anymore. This speed reached by the object is called terminal velocity.

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A train travels due south at 25 m/s (relative to the ground) in a rain that is blown toward the south by the wind. The path of e

olasank [31]

Answer:

Explanation:

Given

Train travels towards south with a velocity if $v_t=25\ m/s$

Rain makes an angle of $\theta =66^{o}$ with vertical

If an observer sees the drop fall perfectly vertical i.e. horizontal component of rain velocity is equal to train velocity

suppose $v_r$ is the velocity of rain with respect to ground then

$v_r\sin\theta =v_t$

$v_r\times \sin (66)=25$

$v_r=27.36\ m/s$

Therefore velocity of rain drops is 27.36 m/s

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3 years ago

19. State any 3 applications of capillary action (3mk)

zlopas [31]

Explanation:

1. Movement of water, food and mineral salts in plants

2. Absorption of water by towels when wiping our bodies

3. It is used to absorb ink using a blotting paper or tissue

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3 years ago

What type of friction is using chalk in the summer to draw on the ground in Copley square?

Lera25 [3.4K]

The second option rolling friction

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3 years ago

An electromagnet is strong enough to lift 200 kg of mass. If you double the number of turns of wire around the core and triple t

VLD [36.1K]

Answer:1200 kg

Explanation:

Given

Electromagnet can lift a mass of $200\ kg$

Magnetic force necessary to hold mass is proportional to Magnetic field

and magnetic field (B) is proportional to NIA

where N=no of turns

I=current in the magnet

A=area of cross-section

When we double the no of turns and triple the current then

N becomes 2 N

I becomes 3 I

therefore magnetic field becomes 6 times

Thus magnetic force becomes 6 times and we can say that electromagnet can hold the 6 times of given weight

i.e. $6\times 200=1200\ kg$

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3 years ago

As a science fair project, you want to launch an 800 g model rocket st raight up and hit a horizontally moving target as it pass

fredd [130]

Sum the forces in the y (upward) direction

$\sum F_y = ma$

$F_t +F_w = ma$

$15N - (0.800kg)(9.81m/s^2) = 0.800kg * a$

$a = 8.94 m/s^2$

Applying the kinematic equations of linear motion we have that the displacement as a function of the initial speed, acceleration and time is

$s = v_0t + \frac{1}{2} at^2$

$30 = 0 +\frac{1}{2} (8.94) t^2$

$t = 2.59 s$

Again through the kinematic equation of linear motion that describes velocity as the change of displacement in a given time, we have to

$v = \frac{d}{t} \rightarrow d = vt$

$d = (15m/s)(2.59s)$

$d = 38.85m$

Therefore the horizontal distance between the target and the rocket should be 38.83m

4 0

3 years ago