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Oksanka [162]
4 years ago
10

How much physical activity do children and teens need? A. 60 minutes at least twice a week B. 60 minutes at least five days a we

ek C. 150 minutes a week D. 150 minutes at least five days a week
Physics
2 answers:
expeople1 [14]4 years ago
7 0

The Answer is A. Teenagers need to exercise at least two times a week for at least 60 minutes.

Len [333]4 years ago
6 0

Answer:

B. 60 minutes at least five days a week

Explanation:

Children and adolescents should do 60 minutes or more of physical activity each day. Most of the 60 minutes should be either moderate- or vigorous intensity aerobic physical activity, and should include vigorous-intensity physical activity at least 3 days a week.

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A motorist makes a trip 180 miles. For the first 90 miles she drives the remaining distance of her speed for the total trip is t
Minchanka [31]

so first your going to use v=Δd/Δt given you the answer 80 i think that's right

3 0
3 years ago
A sled with a mass of 20 kg slides along frictionless ice at 4.5 m/s. It then crosses a rough patch of snow that exerts a fricti
Ugo [173]

Use Newton's second law to determine the acceleration being applied to the sled. There are three forces at work on the sled (its weight, the force normal to the ground, and friction) but two of them cancel, leaving friction as the only effective force. This vector is pointed in the opposite direction of the sled's movement, so if we take the direction of its movement to be the positive axis, we would find the acceleration due to the friction to be

\vec F_G+\vec F_N+\vec F_F=m\vec a\iff-12\,\mathrm N=(20\,\mathrm{kg})a\implies a=-0.6\,\dfrac{\rm m}{\mathrm s^2}

Now we use the formula

{v_f}^2-{v_i}^2=2a(x_f-x_i)

to find the distance it travels. The sled comes to a rest, so v_f=0, and let's take the starting position x_i=0 to be the origin. Then the distance traveled x_f-x_i=x_f is

-\left(4.5\,\dfrac{\rm m}{\rm s}\right)^2=2\left(-0.6\,\dfrac{\rm m}{\mathrm s^2}\right)x_f\implies x_f\approx17\,\mathrm m

6 0
3 years ago
Which of the following objects is in dynamic equilibrium?
Vera_Pavlovna [14]

a. A car driving in a straight line at 20 m/s.

Explanation:

An object is in a state of equilibrium when no force is acting upon it. There are two types of equilibrium; static equilibrium and dynamic equilibrium.

Static equilibrium is a state when a body is at rest.

Dynamic equilibrium is an equilibrium state when a body is moving at a constant velocity. (Rectilinear Motion).

A car moving in a straight line at 20 m/s has a constant velocity and hence no force is acting on it. So, it is in dynamic equilibrium.

A book sitting on a table without moving is not is dynamic equilibrium but in static equilibrium.

A boy jumping off a diving board in not in equilibrium as gravitational force is acting upon him and he has a changing velocity.

A motorcycle going in a circle at a constant speed has changing velocity because the direction of the motion is constantly changing hence it is not in the state of motion.

Keywords: velocity, force, equilibrium, static equilibrium, dynamic equilibrium

Learn more about dynamic equilibrium from brainly.com/question/12880727

#learnwithBrainly

5 0
3 years ago
A 5 meter long ladder leans against a wall. The bottom of the ladder slides away from the wall at the constant rate of 1 3 m/s.
Oksana_A [137]

Answer:9.75 m/s

Explanation:

Given

Length of ladder (L)=5 m

Foot the ladder is moving away with speed of \frac{\mathrm{d} x}{\mathrm{d} t}=13 m/s

From diagram

x^2+y^2=L^2------1

at x=3

y^2=25-9=16

y=4 m

Now differentiating equation 1 w.r.t time

2x\frac{\mathrm{d} x}{\mathrm{d} t}+2y\frac{\mathrm{d} y}{\mathrm{d} t}=0

x\frac{\mathrm{d} x}{\mathrm{d} t}=-y\frac{\mathrm{d} y}{\mathrm{d} t}

3\times 13=-4\times \frac{\mathrm{d} y}{\mathrm{d} t}

\frac{\mathrm{d} y}{\mathrm{d} t}=-\frac{3\times 13}{4}=-9.75 m/s

negative indicates distance is decreasing with time

5 0
3 years ago
A 2.4 kg box has an initial velocity of 3.6 m/s upward along a plane inclined at 27◦ to the horizontal. The coefficient of kinet
Vika [28.1K]

Answer:

d= 1.18 m

Explanation:

In abscense of  friction, total mechanical energy must be constant, i.e.,

ΔK + ΔU = 0

As we are told that there exists a kinetic friction between the box and the plane, we need to take into account the work done by the friction force in the equation, as follows:

ΔK + ΔU = Wnc (1)

If we take as our zero gravitational potential energy reference, the height at which the box is sent upward, we can write the following equations for the different terms in (1):

ΔK = Kf- K₀ = 0 - 1/2*m*v₀² = -1/2*2.4kg* (3.6)²(m/s)² = -15.6 J

ΔU = Uf - U₀ = m*g*h = *m*g*d*sin θ = 2.4 kg*9.81 m/s²*d*0.454 = 10.7*d J

Wnc = Ff. d* cos (180º) = μk*N*d*cos(180º) (2)

The friction force always opposes to the displacement, so the angle between force and displacement is 180º.

The normal force, as is always perpendicular to the surface, takes the value needed to equilibrate the component of the weight perpendicular to the incline, as follows:

N = m*g*cosθ =  2.4 kg*9.81 m/s²*cos 27º = 21 N

Replacing in (2):

Wnc = 0.12*21*cos (180º) = -2.52*d J

Replacing in (1):

-15.6 J + 10.7*d J = -2.52*d J

Solving for d:

d = 1.18 m

 

7 0
4 years ago
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