Susan is driving her car, when traffic ahead of her suddenly stops. She hits her

Question

Susan is driving her car, when traffic ahead of her suddenly stops. She hits her brakes with 100 m between her car and the traffic ahead. If she had been driving at 30 m/s, what acceleration (magnitude) will she need in order to avoid a collision? 0.45 m/s^2 15 m/s^2 4.5 m/s^2 0.15 m/s^2 William throws a ball straight up at 30 m/s, then catches it on its way down. Neglecting air resistance, how fast is the ball going when he catches it? a. It is impossible to answer this question without more information. 10 m/s 9.8 m/s^2 30 m/s

Explanation / Answer

here,

1)

distance , s = 100 m

initial speed , u = 30 m/s

let the magnitude of accelration be a

using third equation of motion

v^2 - u^2 = 2 * a * s

0 - 30^2 = 2 * a * 100

solving for a

a = 4.5 m/s^2

2)

the initial speed of the ball , u = 30 m/s

on its way down

the ball has the same speed and direction is downwards

so the correct option is d) 30 m/s

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