Physics Questions involving velovity, time, acceleration..etc?

Question

Hey! Here are some physics questions that i don't understand, full explanations please. Thank

1. A train travelling at 15ms-1 decelerates at -1.5ms-2 for 5 seconds. What is its new velocity?

2. Escape velocity for a space shuttle leaving earth is 11km sec-1. A very tough astronaut can withstand 10g's without blacking out. (one g is an acceleration of 9.8ms-2). How long a burn must she endure?

3. a high diver takes 2 seconds to hit the water starting from rest. How hight is the diving board?

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Answer 1

1. A train travelling at 15ms-1 decelerates at -1.5ms-2 for 5 seconds. What is its new velocity?

Given a = -1.5m/s^2

t = 5 sec

a = (Vf - Vi)/t

Vf - Vi = a t

Vf = Vi + at

Vf = 15 - 1.5(5)

Vf = 15 - 7.5

Vf = 7.5 m/s

2. Escape velocity for a space shuttle leaving earth is 11km sec-1. A very tough astronaut can withstand 10g's without blacking out. (one g is an acceleration of 9.8ms-2). How long a burn must she endure?

3. a high diver takes 2 seconds to hit the water starting from rest. How hight is the diving board?

t =2 sec

Vi = 0

g = -9.8 m/s2

Find yi (initial height)

yf - yi = Vi t + 1/2 gt^2

0 - yi = 0 + 1/2 (-9.8)(2^2)

-yi = -4.9(4)

yi = 19.6 m