On a summer afternoon, the sand on the beach can get very hot. When you step on the sand in bare feet, you can burn yourself.

2 answers:

8 0

<span>Heat from the Sun is transferred to the sand without direct contact. This heat is then transferred to your feet by direct contact.</span>

topjm [15]3 years ago

7 0

The second sentence best represents the situation because the sun does not touch the sand so direct contact is not made. Then, your feet do touch the sand so direct contact is made. Thus, "Heat from the sun is transferred to the sand without direct contact. This heat is then transferred to your feet by direct contact." is the best answer.

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When a car driving up a hill with constant speed: I. its kinetic energy is decreasing. II. its potential energy is constant. III

madam [21]

A car driving up a hill at a constant speed experiences no change in its kinetic energy while it's potential energy increases with increasing height, thus none of the options are correct.

Understanding the concept

Consider a car moving up the hill at a constant speed as shown in the figure below. The following forces act on the car:

N is the normal reaction force acting in an upward direction

f_s is the static friction force exerted due to friction between the road and the tires of the car
f_k is the rolling friction force in the direction opposing that of the tire
mg is the force acting in a downward direction.

θ is the angle of inclination.

Here as the car is moving up the hill at a constant speed, the net force exerted on the car is zero. Also, the kinetic energy of the car will not change as its velocity is constant and the potential energy will change with increasing height. Thus, none of the given options are correct.

Learn more about motion on an incline here:

<u>brainly.com/question/13513083</u>

#SPJ4

5 0

2 years ago

What is the intensity in W/m2 of a laser beam used to burn away cancerous tissue that, when 85.0% absorbed, puts 470 J of energy

Advocard [28]

Answer:

26036485.6433 W/m²

Explanation:

E= Energy = 470 J

t = Time = 4 seconds

d = Diameter = 2.6 mm

Power is given by

$P=\dfrac{E}{t}$

Intensity is given by

$I=\dfrac{P}{\pi r^2}\\\Rightarrow 0.85I=\dfrac{E}{t\dfrac{\pi}{4} d^2}\\\Rightarrow I=\dfrac{470}{0.85\times 4\times \dfrac{\pi}{4}\times (2.6\times 10^{-3})^2}\\\Rightarrow I=26036485.6433\ W/m^2$