Question

Please help, thank you! I would like to know how to answer these and understand them.. Thank you so much. I've been trying to figure them out, and I feel like I got the answer, but my answer didn't match with any of the answers so now I'm really unsure....
A penny is thrown from a 1000.0 m building with an initial velocity of 2.00 m/s down.
What is the penny’s velocity after 3.00 s?

a. −31.4 m/s
b. −3.10 m/s
c. −90.3 m/s
d. −9.00 m/s

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A penny is thrown from a 1000.0 m building with an initial velocity of 2.00 m/s down.
How far will the penny fall in 10.0 s?

a. −69 m
b. −118 m
c. −511 m
d. −1000 m

Answer 1

1) The penny's velocity after 3.00 s is -31.4 m/s

2) The displacement of the penny is -510 m

Explanation:

1)

The motion of the penny is a motion of free fall, since only the force of gravity acts on it. So it is a motion with uniform acceleration, therefore we can use the following suvat equation:

$v=u+at$

where:

v is the final velocity

u is the initial velocity

a is the acceleration

t is the time

Here we have, by chosing upward as positive direction:

u = -2.0 m/s (initial velocity)

$a=g=-9.8 m/s^2$ (acceleration of gravity)

And substituting t = 3.00 s, we find the velocity of the penny at t = 3.00 s:

$v=(-2.0)+(-9.8)(3.0)=-31.4 m/s$

2)

We can solve this part by using the following suvat equation:

$s=ut+\frac{1}{2}at^2$

where

s is the displacement

u is the initial velocity

a is the acceleration

t is the time

Substituting:

u = -2.0 m/s

$a=g=-9.8 m/s^2$

and t = 10.0 s, we find the displacement of the penny after 10 seconds:

$s=(-2.0)(10.0)+\frac{1}{2}(-9.8)(10.0)^2=-511 m$

Learn more about free fall motion:

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