Question

Alexander's hobby is dirt biking. On one occasion last weekend, he accelerated from rest to 17.8 m/s in 1.56 seconds. He then maintained this speed for 9.47 seconds. Seeing a coyote cross the trail ahead of him, he abruptly stops in 2.79 seconds. Determine Alexander's average speed for this motion.

Answer 1

HEllo @supergurl !

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Answer 2

Let's do this one !

Do u know the equations of motion ?

Answer 3

ok..so can u calculate the distance traveled in going from rest to 17.8 m/s in 1.56 s using second equation of motion ?

Answer 4

s=ut + \(\large\sf \frac{1}{2}at^2\)

Answer 5

u=0
v=17.8
t=1.56
a=? (calculate a first by using v=u+at)

Answer 6

Getting the hints ?

Answer 7

a=11.4 m/s/s

Answer 8

ok now calculate s using
s=ut + \(\large\sf \frac{1}{2}at^2\)

Answer 9

13.8m

Answer 10

CORRECT !
Good going

Answer 11

Now he maintained this speed for 9.47 seconds. So calculate the distance traveled during this period using Distance = Speed \(\times\) Time

Answer 12

169 m

Answer 13

Brilliant !
\(\huge\checkmark\)

Answer 14

Now he starts braking/deaccelerating, so let's first calculate his deacceleration or breaking force bu using v=u-at (note the minus sign in case of deacceleration). Take v=0 (as the bike stopped finally), u=17.8 and t=2.79s

Answer 15

???

Answer 16

a= -6.38 m/s/s

Answer 17

\(\huge\checkmark\)

Finally calculate the distance traveled during this period. You can use either
s=ut + \(\large\sf \frac{1}{2}at^2\) or \(\large \sf v^2 = u^2 + 2as\)

Answer 18

s=24.8 m

Answer 19

Great !
We are almost done !

Now we know all the distances and all the times. Average speed = Total distance coverd/Total time taken

Answer 20

Last Step:

Average speed = (24.8+169+13.8)/(1.56+9.47+2.79)

Answer 21

207.6m/13.82s = 15 m

Answer 22

thank you so much for your help! :)

Answer 23

15.02 m/s

Answer 24

\(\color{red}{\huge\bigstar}\huge\text{You're Most Welcome! }\color{red}\bigstar\)
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Answer 25

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Answer 26

\(\color{blue}{\text{Originally Posted by}}\) @supergurl
207.6m/13.82s = 15 m (it should be m/s)
\(\color{blue}{\text{End of Quote}}\)

Answer 27

ah thanks for catching my mistake

Answer 28

\(\huge\sf\color{green}{\text{✌ﾟ\(\ddot\smile\) ✌ﾟ}}\)