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3 years ago

14

If every action has an equal and opposite reaction, then when you jump, and gravity pulls you back down, it also pulls the Earth

up to you. Why can’t you see this motion?

1 answer:

LenKa [72]3 years ago

8 0

When two objects are gravitationally attracted, the forces

on both of them are equal. As the objects move straight

toward each other, then, just as we'd expect, the object

with the greater mass has the smaller acceleration and

moves a smaller distance by the time they collide, while

the object with a smaller mass has the greater acceleration

and moves a greater distance by the time they collide.

The Earth's mass is roughly approximately something like 70,000,000,000,000,000,000,000 times as much as YOUR mass,

so the difference in acceleration and distance moved before

the collision is really substantial.

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A raft is made of 12 logs lashed together. Each is 45 cm in diameter and has a length of 6.5 m. How many people can the raft hol

tatyana61 [14]

Answer:

324 people

Explanation:

radius r = diameter / 2 = 45cm /2 = 22.5 cm or 0.225 m

We can calculate the total volume of the log by computing the volume of each cylindrical log:

$V = \pi r^2 L = \pi 0.225^2 * 6.5 = 4.6 m^3$

So the total volume of all 12 logs is

$12 * 4.6 = 55.135 m^3$

The weight that the raft can support, is the buoyancy force subtracted by its own weight.

The buoyancy force is basically the weight of the water is displaced, which is water density times volume. The log weight is also log density times its volume

$F = F_b - F_w = g\rho_wV - g\rho_rV = gV(\rho_w - \rho_r)$

where $\rho_w = 1000kg/m^3,\rho_r$ are the density of water and raft, respectively. But since we have the specific gravity of wood is 0.6. That measn

$\rho_r / \rho_w = 0.6$

$\rho_r = 0.6\rho_w$

Therefore $\rho_w - \rho_r = \rho_w - 0.6\rho_w = 0.4\rho_w = 0.4*1000 = 400 kg/m^3$

Let g = 9.8m/s2. We can now calculate the force that the raft can support

$F = gV(\rho_w - \rho_r) = 9.8*55.135*400=216129.2N$

Each person has a mass of 68kg, their weight would be

W = 68*g = 68*9.8 = 666.4N

So the maximum number of people that the raft can hold is

F / W = 216129.2 / 666.4 = 324 people

3 0

3 years ago

The ideal mechanical advantage of a machine reflects the increase or decrease in force there world be without friction, it is al

brilliants [131]

True: the ideal mechanical advantage of a machine is always greater than the actual mechanical advantage because all machines must overcome friction.

Explanation:

For a simple machine, it is possible to calculate two types of mechanical advantage:

1) The Ideal Mechanical Advantage (IMA) is given by

$IMA=\frac{d_e}{d_r}$

where

$d_r$ is the resistance arm

$d_e$ is the effort arm

The IMA gives the mechanical advantage of the machine if there are no friction forces acting on it, and if all the work in input is converted into work in output with no loss of energy

2) The Actual Mechanical Advantage (AMA) is given by

$AMA=\frac{L}{E}$

where

L is the load (the force in output)

E is the effort (the force in input)

The AMA gives the real mechanical advantage of the machine. For an ideal machine,

$AMA=IMA$

Because there is no loss of energy due to friction.

For a real machine instead,

$AMA$

because part of the input energy is converted into thermal energy and other forms of energy due to the presence of friction, so it is "wasted" energy.

Learn more about levers and machines:

brainly.com/question/5352966

#LearnwithBrainly

8 0

3 years ago

If a copper tube has current flowing to the right in the presence of a magnetic field going forward ("into the board"), we expec

Citrus2011 [14]

Answer:

False, because current flow has no effect in the weight of a conductor.

Explanation:

Current flow has no effect in the weight of a conductor. Thus, the weight on the scale will be the same when current is flowing and when current is not flowing in the copper tube.

Therefore, If a copper tube has current flowing to the right in the presence of a magnetic field going forward ("into the board"), we expect the weight on the scale to be the same whether current is flowing or not.

6 0

3 years ago

Liquids with convex meniscus

kobusy [5.1K]

Mercury in a glass tube.

7 0

2 years ago

A lion has a mass of 45 kg. Answer the following questions about it, using correct units. a. The lion runs at a speed of 14.2 m/

Eva8 [605]

A) The kinetic energy of an object is given by:
$K= \frac{1}{2}mv^2$
where m is the mass of the object, and v its speed. For the lion in our problem, m=45 kg and v=14.2 m/s, so its kinetic energy is
$K= \frac{1}{2}mv^2= \frac{1}{2}(45 kg)(14.2 m/s)^2=4537 J$

b) the increase in gravitational potential energy of the lion is given by:
$\Delta U = mg \Delta h$
where g is the gravitational acceleration, and $\Delta h$ is the increase in altitude of the lion. In this problem, $\Delta h=28 m$ , so the increase in gravitational potential energy is
$\Delta U=mg \Delta h=(45 kg)(9.81 m/s^2)(28 m)=12361 J$

c) When the fox reaches the top of the tree, its gravitational potential energy is
$U=mgh=(1.8 kg)(9.81 m/s^2)(3.8 m)=67 J$
As it jumps, its kinetic energy is
$K= \frac{1}{2}mv^2= \frac{1}{2}(1.8 kg)(8.1 m/s)^2=59 J$
So the total mechanical energy of the fox as it jumps is
$E=U+K=67 J + 59 J =126 J$

6 0

3 years ago