# Project #80536 - physics 1

1)

A dog runs back and forth between its two owners, who are walking

toward each other as seen in the figure below:

The

dog starts running when the owners are 10.0 m apart. If the dog runs

with a speed of 3.0 m/s, and the owners each walk with a speed of 1.3

m/s, how far has the dog traveled when the owners finally meet in the

middle?

2)

A

train accelerates away from a train station and reaches a speed of 4.7

m/s in 5.0 s. If the train’s acceleration remains constant, what will its

speed be after an additional 6.0 s (after 5 s) has elapsed?

3)

In July of 1977, racecar driver David

Purley

which his car’s throttle was jammed “wide open,” meaning his car would

only allow the throttle to be completely down. As a result, he crashed into

a wall at an amazing 173 km/

hr

and was “decelerated” down to 0 km/

hr

within a distance of only 0.66 m. If we assume his acceleration was

constant, calculate the magnitude of the acceleration David experienced

during this crash. Express your answer in terms of “g’s,” that is, in terms of

the acceleration due to gravity: g=9.81 m/s

2

. To date, David’s crash is the

most severe “g

-

force” ever experienced by a human being who still survived.

4)

A bicyclist is finishing his repair of a flat tire when a friend rides by with a

constant speed of 3.5 m/s. Two seconds later the bicyclist hops on his bike and

accelerates at 2.4 m/s

2

until he manages to catch his friend.

(a) How

much time does it take for the bicyclist to catch his friend?

(b) How

far does he have to travel to catch his friend?

(c) What

is the bicyclist’s speed when he catches his friend?

5)

A simple way to test reaction times is to have someone drop a ruler in between

your two fingers and you catch it as quickly as you can.

(a) If

the ruler starts at one end (0 cm), and you catch it with your fingers on the

7.5 cm mark, what is your reaction time?

(b) If

the best human reaction times are around 0.10 s, would you be willing to set

up a game using the same experiment with a \$100 dollar bill, which is about 15 cm

in length? The point of the game is you hold the \$100 dollar bill while the “player”

has their fingers at the exact middle of the bill. You then drop it, and if the player

manages to catch the \$100 bill, they get to keep it...if they don’t, they owe you \$5.

 Subject Science Due By (Pacific Time) 08/31/2015 02:00 am
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