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3 years ago

If an object starts out at rest and accelerates to 100 m/s, what is its initial speed?

1 answer:

6 0

No. Sadly, you're not right. The whole problem here is the meaning of a few words. "Starts out"is the same thing as "initial" conditions. "At rest" is the same thing as not moving ... zero speed. So if an object starts out at rest, that says that its initial speed is zero ... choice 'b'.

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The Stronger the force that is exerted on an object,the ____ the change in velocity will be.

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3 years ago

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A girl throws a pebble into a deep well at 4.0 m/s (downward). It hits the water in 2.0 s. How far below the ground is the water

alexandr402 [8]

Answer:

27.6 m
13.8 m/s

Explanation:

(b) The initial velocity is added to that due to acceleration by gravity. The velocity is increased linearly by gravity at the rate of 9.8 m/s². The average velocity of the pebble will be its velocity halfway through the 2-second time period.* That is, it will be ...

4 m/s + (9.8 m/s²)(2 s)/2 = 13.8 m/s . . . . average velocity

(a) The distance covered in 2 seconds at an average velocity of 13.8 m/s is ...

d = vt

d = (13.8 m/s)(2 s) = 27.6 m

The water is about 27.6 m below ground.

_____

* We have chosen to make use of the fact that the velocity curve is linear, so the average velocity is half the sum of initial and final velocities:

vAvg = (vInit + vFinal)/2 = (vInit + (vInit +at))/2 = vInit +at/2

If you work this in a straightforward way, you would find distance as the integral of velocity, then find average velocity from the distance and time.

$\displaystyle d=\int_0^t{(v_0+at)}\,dt=v_0t+\dfrac{1}{2}at^2=t\left(v_0+a\dfrac{t}{2}\right)\\\\v_{avg}=\dfrac{d}{t}=v_0+a\dfrac{t}{2}\qquad\text{the formula we started with}$

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3 years ago

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3 years ago

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gayaneshka [121]

B or C i think its B.

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3 years ago

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4) T F If two objects have the same moment of inertia, they must have the same mass.

lisov135 [29]

Answer:

False

Explanation:

The moment of inertia for a rigid body is given by

$I=\int \rho(r) r^2 dV$

where

$\rho(V)$ is the density distribution of the object

r is the distance from the axis of rotation of the object

Essentially, the moment of inertia does not depend only on the mass of the object, but also on its shape. For example: for a solid cylinder, the moment of inertia derived from the formula above is

$I=\frac{1}{2}MR^2$

where M is the mass of the cylinder and R is its radius. As we see, I (moment of inertia) does not depend on the mass only: therefore, if two objects have same moment of inertia, this does not imply that they also have the same mass.

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4 years ago