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3 years ago

You toss a ball in the air. what is the work done by gravity as the ball goes up?

1 answer:

7 0

Answer: Gravity slows the ball down as it goes up and eventually stops it from going up and starts to pull it back down to earth.

Explanation:

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When a board with a box on it is slowly tilted to larger and larger angle, common experience shows that the box will at some poi

eimsori [14]

Answer: The force of kinetic friction is smaller than that of static friction, but F_g remains the same.

Explanation:

The situation is same as when a book is pushed with an increasing force on a table; When the force is low, book doesn't move, until that under a given force starts moving, and then it goes on movement even if the force decreases a bit.

The physical explanation for this, that friction force adopts any value needed to avoid to move the object, till a limit value is achieved, called static friction force, equal to the normal force times the static friction coefficient.

Once in movement, the kinetic friction coefficient replaces the static one , and in general is lower than the static one, so the force diminishes.

In the case of the box sliding down the board, the force that tries to move the object down the board, is the component of the weight parallel to the board, that can be showed that being equal to the weight times the sinus of the angle of the board with the horizontal, as follows:

F_g = m g sin θ

When θ increases, F_g does the same, so friction force always has the same magnitude than F_g (but opposite direction) so the box doesn't move, till that θ takes a value that produces a F_g equal to static friction force.

Beyond this limit angle, F_g (remaining the same for a given angle) is greater than the kinetic friction force, and the box slides.

In the limit, when θ=90º, sin θ =1⇒ F_g = mg, so the object is in free fall.

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3 years ago

Which is true about surface waves?

Sauron [17]

The disturbance does not have a specific motions

7 0

3 years ago

Read 2 more answers

A person jumps off a diving board 5.0 m above the water's surface into a deep pool. The person's downward motion stops 2.2 m bel

shutvik [7]

Answer:

9.9 m/s

Explanation:

t = Time taken

u = Initial velocity

v = Final velocity

s = Displacement

a = Acceleration due to gravity = 9.81 m/s²

$v^2-u^2=2as\\\Rightarrow v=\sqrt{2as+u^2}\\\Rightarrow v=\sqrt{2\times 9.81\times 5+0^2}\\\Rightarrow v=9.9\ m/s$

If the body has started from rest then the initial velocity is 0. In order to find the velocity just before hitting the water then the distance at which the downward motion stops is irrelevant.

Hence, the speed of the diver just before striking the water is 9.9 m/s

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3 years ago

A block sliding across a level surface has a mass of 2.5 kg and a mechanical energy of 20 joules. What is its velocity?

tia_tia [17]

Hi!

The energy of the block is 4 m/s

To calculate this, you need to use the equation for kinetic energy. The block is sliding (i.e. it's moving). If the object is sliding across a level surface, the only energy it has is kinetic energy, because there is no change in potential energy (which changes with height). So, the mechanical energy will be pure kinetic energy. The equation is the following, derived from the expression for kinetic energy:

$v= \sqrt{ \frac{2*Ke}{m}}=\sqrt{ \frac{2*20 (kg*m^{2}*s^{-2}) }{2,5kg}}=4 m/s$

Have a nice day!

8 0

3 years ago

Physical activity is the most important thing you can do to improve and maintain health-related physical fitness. Which list con

katovenus [111]

Answer:

I guess it's d because age environment heredity Nd maturation r more obvious factors if we compre with only physical fitness

8 0

3 years ago