PHYSICS
HIGH SCHOOL

Answer:

A stone weighing 1.5 kilograms is resting on a rock at moss which is at a height of 10m whose gravitational potential energy is 147 J.

What is gravitational Potential Energy ?Gravitational potential energy is an energy acquired by an object due to a change in its height when it is present in a gravitational field. It is denoted by P or U. and it its expressed in joule. Gravitational potential energy is given by U = mgh where m is the mass of the object, g is acceleration due to gravity and h is the height.

when we take an object of mass m to a certain height in the field of gravitation, we can say that body has potential energy and we release that body from that height, it falls.

Given,

Weight = 1.5 kg = 1.5*9.8 N = 14.7 N.

height = 20 m to 10 m.

Potential Energy U = ?

Stone has come to the moss where it has height 10m and we have to find P.E. there. si height is 10m

P.E. = mgh = 14.7*10 = 147 Joules

Hence potential energy of the stone is 147 J.

To know more about Potential energy :

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Answer: We can ignore all that business about resting on the rock and

rolling down part of the way and then resting on the moss.

Its potential energy right now doesn't depend on what happened

to it yesterday. We don't care.

All we care about is that we're walking along in the park and we

notice a 1.5kg rock lying in moss 10 meters above the ground.

Gravitational potential energy

= (mass) · (gravity) · (height)

= (1.5 kg) · (9.8 N/kg) · (10 m)

= 147 (kg · N · m / kg)

= 147 joules

rolling down part of the way and then resting on the moss.

Its potential energy right now doesn't depend on what happened

to it yesterday. We don't care.

All we care about is that we're walking along in the park and we

notice a 1.5kg rock lying in moss 10 meters above the ground.

Gravitational potential energy

= (mass) · (gravity) · (height)

= (1.5 kg) · (9.8 N/kg) · (10 m)

= 147 (kg · N · m / kg)

= 147 joules

COLLEGE

On a cold day, a heat pump absorbs heat from the outside air at 14°F (−10°C) and transfers it into a home at a temperature of 86°F (30°C). Determine the maximum κ of the heat pump.

Answer:

6.575

Explanation:

T1 = 30C = 30 + 273 = 303 K

T2 = - 10 C = - 10 + 273 = 263 K

The coefficient of performance of heat pump

k = T2 / (T1 - T2)

k = 263 / (303 - 263) = 6.575

COLLEGE

A lightbulb has a power of 100 W. and is used for 4 hours. A microwave has a power of 1200 W and is used for 5 minutes. a. How much energy is used by the lightbulb?

b. How much energy is used by the microwave?

c. The lightbulb has an efficiency of 1.8%. How much heat energy does the lightbulb produce in 4 hours?

a) E=Nt=100*(4*3600)=1440000 J

b) E=1200*(5*60)=360000 J

c) Q=E*(100-1.8)/100=1414080 J

HIGH SCHOOL

A vector has an x-component of length 8 and a y-component of length 2. What is the angle of the vector? (Hint: Use the inverse tangent.)

Answer:

14.04 deg

Explanation:

Consider a right triangle ABC whose hypotenuse represent the vector itself.

x = x-component of the vector = adjacent "BC" of triangle ABC = 8

y = y-component of the vector = opposite "AC" of triangle ABC = 2

θ = angle of the vector

In triangle ABC, using trigonometric ratio

tanθ = AC/BC

tanθ = 2/8

tanθ = 0.25

θ = tan⁻¹(0.25)

θ = 14.04 deg

Θ = tan⁻¹(2/8) = 14.03°

HIGH SCHOOL

During a tennis match, a player serves the ball at 27.4 m/s, with the center of the ball leaving the racquet horizontally 2.34 m above the court surface. The net is 12.0 m away and 0.900 m high. When the ball reaches the net, (a) what is the distance between the center of the ball and the top of the net? (b) Suppose that, instead, the ball is served as before but now it leaves the racquet at 5.00° below the horizontal. When the ball reaches the net, what now is the distance between the center of the ball and the top of the net? Enter a positive number if the ball clears the net. If the ball does not clear the net, your answer should be a negative number. Use g=9.81 m/s2.

a. The ball's horizontal and vertical positions at time are given by

The ball reaches the net when :

At this time, the ball is at an altitude of

which is 1.40 m - 0.900 m = 0.500 m above the net.

b. The change in angle gives the ball the new position functions

The ball reaches the net at time such that

at which point the ball's vertical position would be

so that the ball does not clear the net with 0.343 m - 0.900 m = -0.557 m.