An 18-year-old runner can complete a 10.0-km course with an average speed of 4.3
ID: 1528518 • Letter: A
Question
An 18-year-old runner can complete a 10.0-km course with an average speed of 4.33 m/s. A 50-year-old runner can cover the same distance with an average speed of 4.17 m/s. How much later (in seconds) should the younger runner start in order to finish the course at the same time as the older runner? A motorcycle has a constant acceleration of 3.66 m/s. Both the velocity and acceleration of the motorcycle point in the same direction. How much time is required for the motorcycle to change its speed from (a) 24.6 to 34.6 m/s, and (b)54.6 to 64.6 m/s?Explanation / Answer
Q-1)
Given Data
The total distance is S = 10.0km =10*103 m
The speed of the 18-year-old runner is V18 = 4.33 m/s
The speed of the 50-year-old runner is V50 = 4.17 m/s
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Time taken by 18-year-old to travel the distance S is t1 = S / V18
= 10*103m / 4.33 m/s
= 2309.47 s
Time taken by 50-year-old to travel the distance S is t2 = S / V50
= 10*103m / 4.17 m/s
= 2398.08 s
Then the difference in time is t = t2 -t1
= 2398.08 – 2309.47
= 88.61 s
Q-2) V = a*t
=> t = V / a
=> t = (V2 – V1) / a
a) t = (V2 – V1) / a
t = (34.6 – 24.6) / 3.66
t = 2.73 s
b) t = (V2 – V1) / a
t = (64.6 – 54.6) / 3.66
t = 2.73 s
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