Lisa gives her little brother Sam a 15-second (sec) head start in a 300-meter (m) race. During the race. Sam runs at an average speed of 5 m/sec and Lisa runs at an average speed of 8 m/sec, not including the head start. Since the time Lisa started running, what is the best approximates the number of seconds that had passed when Lisa caught up to Sam?

Shohan

12 views

2025-01-04 04:42

1 Answers

Shohan

$S a m r u n s a h e a d o f L i s a i n 15 s e c o n d s = 5 x 15 = 75 m H e r e, L i s a' s a v e r a g e s p e e d = 8 m s^{- 1} A n d S a m' s a v e r a g e s p e e d = 5 m s^{- 1} ∴ L i s a' s s p e e d i s = 8 - 5 = 3 m s^{- 1} m o r e t h a n t h a t o f S a m$

$∴ T i m e t a k e n b y L i s a t o c a t c h u p S a m$

$= \frac{75 m}{3 m s^{- 1}} [A s, t = \frac{d}{v}]$

$= 25 s e c o n d s$

$∴ T o t a l t i m e t a k e n b y L i s a t o c a t c h s u m u p$

$= 25 + 15 = 40 s e c o n d s$

12 views Answered 2024-12-14 13:31

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