Which of the following statements about average speed is correct? A) The average

Question

Which of the following statements about average speed is correct? A) The average speed is equal to the magnitude of the average velocity. B) The average speed can never be greater than the magnitude of the average velocity. c) The average speed can never be less than the magnitude of the average velocity. D) If the average speed is zero, the average velocity may be greater than or less than zero. E) If the average velocity is zero, then the average speed must be zero. A ball is thrown straight up with a velocity of +20 m/s. At the end of 3 s, its velocity will be close to A) -50 m/s B) -30 m/s C) -20 m/s D) -10 m/s E) +10 m/s An object starts from rest and accelerates uniformly. If it moves 2 m during the first second, then during the first 4 seconds, it will move A) 6 m B) 8 m C) 10 m D) 18 m E) 32 m A ball rolls off a horizontal shelf a height h above the floor and takes 1.0 s to hit. For a ball to take 3.0 s to reach the floor, the shelf's height above the floor would have to be A) 2h B) 3h C) (Squareroot 3)h D) 4h E) 9h A frog leaps vertically into the air and encounters no appreciable air resistance. Which statement about the frog's motion is correct?

Explanation / Answer

1. average speed can never be smaller than average velocity beacuse average velocity deals with net displacement and average speed deals with total distance and as we know displacement can never be greater than distance, so average velocity always less or equal to average speed.

option(c) is correct

2.v= u+gt= 20-10*3= -10 m/s

option (d) is correct

3. using 2nd equation of motion

s= 0.5* at*t

2= 0.5* a*1*1

a= 4 m/s/s

now again using 2nd equation of motion

d= 0.5*at*t= 0.5* 4* 4*4= 32 m

option (e)

4.

h= 0.5gt*t

at t= 1

h= 0.5 g ...(i)

now for other height,

H= 0.5g(3*3)

from ...(i)

H= 9h

option (e)

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