Remains of ancient life are most often preserved through which process?

A man pushes a shopping cart across a level floor. What force resists the effort force? A) gravity B) friction C) the normal for

Kipish [7]

Answer:

B) Friction

Explanation:

Friction is a force that acts when an object is sliding along a surface. Microscopically, this force is due to the fact that the two surfaces are not perfectly smooth, but they have "imperfections" that cause a force that opposes the motion of the object.

For an object sliding on a flat surface, the force of friction has magnitude:

$F_f = \mu_k mg$

where

$\mu_k$ is the coefficient of kinetic friction

m is the mass of the object

g is the acceleration of gravity

The direction of the force of friction is always opposite to the direction of motion of the object.

In reality, friction also acts if the object is at rest and it is pushed by a force; in this case, we talk about static friction, and its magnitude is

$F_f = \mu_s mg$

where $\mu_s$ is called coefficient of static friction, and it is generally larger than the coefficient of kinetic friction.

8 0

3 years ago

If a thermometer measured the temperature in an oven as 400oF five days in a row when the temperature was actually 397oF, this m

aleksandrvk [35]

Answer:

It can be said to be reliable although it is not valid

Explanation:

This is because Reliability means an indicator of consistency, A measure should produce similar or the same results consistently if it measures the same quantity. So does the thermometer measures over 5days but it is not valid because it deviates from the real value

5 0

3 years ago

How fast (in rpm) must a centrifuge rotate if a particle 7.3 cm from the axis of rotation is to experience an acceleration of 1.

guajiro [1.7K]

The formula we use here is:

radial acceleration = ω^2 * R 

110,000 * 9.81 m/s^2 = ω^2 * 0.073 m
ω^2 = 110,000 * 9.81 / 0.073
ω = 3844.76 rad/s

and since: ω = 2pi*f --> f = ω/(2pi)
f = 3844.76 / (2pi) = 611.91 rps = 611.91 * 60 rpm
= 36,714.77 rpm

5 0

3 years ago

A train is moving in a straight railway where it covered one third of the distance with

Alexxandr [17]

Answer:

The average speed of the train is 45 km/h

Explanation:

Speed

It's defined as the distance (d) per unit of time (t) traveled by an object. The formula is:

$\displaystyle v=\frac{d}{t}$

Let's call x the total distance covered by the train. It covered d1=1/3x with a speed of v1=25 km/h. The time taken is calculated solving for t:

$\displaystyle t_1=\frac{d_1}{v_1}$

$\displaystyle t_1=\frac{1/3x}{25}$

$\displaystyle t_1=\frac{x}{75}$

Now the rest of the distance:

d2 = x - 1/3x = 2/3x

Was covered at v2=75 km/h. Thus the time taken is:

$\displaystyle t_2=\frac{d_2}{v_2}$

$\displaystyle t_2=\frac{2/3x}{75}$

$\displaystyle t_2=\frac{2x}{225}$

The total time is:

$\displaystyle t_t=\frac{x}{75}+\frac{2x}{225}$

$\displaystyle t_t=\frac{3x}{225}+\frac{2x}{225}$

$\displaystyle t_t=\frac{5x}{225}$

Simplifying:

$\displaystyle t_t=\frac{x}{45}$

The average speed is the total distance divided by the total time:

$\displaystyle \bar v=\frac{x}{\frac{x}{45}}$

Simplifying:

$\boxed{\displaystyle \bar v=45\ km/h}$

The average speed of the train is 45 km/h

5 0

3 years ago

Draw the following vector quantity Using the coordinate system.

DiKsa [7]

The given vectors quantities can be described by their properties of both

magnitude and direction.

a. The drawing of the vector extending from point (0, 0) to (190, 0) on the coordinate plane is attached.

b. The velocity vector extending from (0, 0) to (108.76, 50.714) on the coordinate plane is attached.

c. The displacement vector extending from (0, 0) to (30·√2, 30·√2) is attached.

Reasons:

a. The magnitude of the vector = 190 N

The direction in which the vector acts = East

Therefore, in vector form, we have;

$\vec{F}$ = 190 × cos(0)·i + 190 × sin(0)·j = 190·i

The vector can be represented by an horizontal line, 190 units long

Coordinate points on the vector = (0, 0) and (190, 0)

The drawing of the vector with the above points using MS Excel is attached.

b. Magnitude of the velocity vector = 120 km/hr. 25° North of east

Solution;

The vector form of the velocity is; $\vec{v}$ = 120 × cos(25)·i + 120×sin(25)·j, which gives;

$\vec{v}$ = 120 × cos(25)·i + 120×sin(25)·j ≈ 108.76·i + 50.714·j

$\vec{v}$ ≈ 108.76·i + 50.714·j

Therefore, points that define the vector are; (0, 0) and (108.76, 50.714)

The drawing of the vector is attached

c. The magnitude of the vector = 60 m

The direction of the vector is southwest = West 45° south

The vector form of the displacement is $\vec{d}$ = 60 × cos(45°)·i + 60 × sin(45°)·j

Which gives;

$\vec{d}$ = 30·√2·i + 30·√2·j

Points on the vector are therefore; (0, 0), and (30·√2, 30·√2)

The drawing of the vector is attached

Learn more about vectors here:

brainly.com/question/10409036

4 0

2 years ago