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3 years ago

a car traveling at 28 m/s slows down at a constant rate for 4 seconds until it stops. what is its acceleration?

1 answer:

3 0

We are given the following conditions:
$v_{0} = 28m/s

t = 4s

v_{f} = 0m/s$

Since we are told it slows down at a constant rate, we know we are dealing with uniformed accelerated motion, or UAM for short.

So we look at our kinematics equation that contains the given variables.

$v_f = v_0 + at$

This contains our target variable and our initial conditions. Plug and chug, we get:

$(0m/s) = (28m/s) + a(4s) -28m/s = (4s)*a a = -7m/s^2$

Thus the answer is:

a = -7m/s^2

Hope this helps!

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A 3.00N rock is thrown vertically into the air from the ground. At h=15.0m, v=25m/s upward. Use the work-energy theorem to find

butalik [34]

Answer:

so initial speed of the rock is 30.32 m/s

correct answer is b. 30.3 m/s

Explanation:

given data

h = 15.0m

v = 25m/s

weight of the rock m = 3.00N

solution

we use here work-energy theorem that is express as here

work = change in the kinetic energy ..............................1

so it can be written as

work = force × distance ...................2

and

KE is express as

K.E = 0.5 × m × v²

and it can be written as

F × d = 0.5 × m × (vf)² - (vi)² ......................3

here

m is mass and vi and vf is initial and final velocity

F = mg = m (-9.8) , d = 15 m and v{f} = 25 m/s

so put value in equation 3 we get

m (-9.8) × 15 = 0.5 × m × (25)² - (vi)²

solve it we get

(vi)² = 919

vi = 30.32 m/s

so initial speed of the rock is 30.32 m/s

5 0

3 years ago

A fireman of 80 kg slides down a pole.When he reaches the bottom, 4.2 m below his starting point, his speed is 2.2 m/s . By how

levacccp [35]

Answer:

3099 J

Explanation:

The increase in thermal energy corresponds to the mechanical energy lost in the process.

The mechanical energy is given by the sum of gravitational potential energy and kinetic energy of the fireman:

$E=K+U$

At the top of the pole, the fireman has no kinetic energy, so all his mechanical energy is just potential energy:

$E=U=mgh=(80 kg)(9.8 m/s^2)(4.2 m)=3293 J$

When the fireman reaches the bottom, he has no gravitational potential energy, so his mechanical energy is just given by his kinetic energy:

$E=K=\frac{1}{2}mv^2=\frac{1}{2}(80 kg)(2.2 m/s)^2=194 J$

So, the loss in mechanical energy was

$\Delta E=3293 J-194 J=3099 J$

and this corresponds to the increase in thermal energy.

7 0

2 years ago

What is a true statement about the rotation period of the moon?

mrs_skeptik [129]

The time it takes for the Moon to rotate once around its axis is equal to the time it takes for the Moon to orbit once around Earth

5 0

2 years ago

Which of the following changes would remove the source of energy that generates the convection which makes wind here on Earth?

alukav5142 [94]

Answer:blocking all solar radiation

Explanation:

google has it

4 0

2 years ago

A pendulum swings in an arc in which each successive swing is 40% as long as the previous swing. if the first swing covers an ar

nlexa [21]

The situation given above is that of the geometric sequence with first term equal to 75 meters and the common ratio equal to 0.40. The sum of the terms for an infinite geometric sequence is expressed in the equation,
S = a1/(1 - r)
Substituting,
S = (75 m) / (1 - 0.4) = 125 m
Therefore, the total distance that the pendulum had swung before finally coming to rest is 125 m.

8 0

3 years ago