Question

Lavanya throws a ball upwards, from a rooftop, which is 20 m above from ground. It will reach a maximum height
and then fall back to the ground. The height of the ball from the ground at time is h, which is given by h=-4t+16+ + 20.
(i) What is the height reached by the ball after 1 second?
(a) 64 m (C) 32 m (b) 128 m (d) 20 m

(ii) What is the maximum height reached by the ball?
(a) 54 m (c) 36 m (b) 44 m (d) 18 m

(iii) How long will the ball take to hit the ground?
(a) 4 seconds (c) 5 seconds (b) 3 seconds (d) 6 seconds

(iv) What are the two possible times to reach the ball at the same height of 32 m?
(a) I and 3 seconds (c) I and 2 seconds

(v) Where is the ball after 5 seconds
(a) at the ground (c) at highest point (b) 1 and 4 seconds (d) 1 and 5 seconds (b) rebounds (d) fall back​

Answer 1

Answer:

a. -16(1)2 + 64(1) + 80

    -16 + 64 + 80 = 128

 

b. x = -b/2a = -64/(2(-16)) = 2

y = -16(2)2 + 64(2) + 80

     -64 + 128 + 80 = 144

 

c. -16t2 + 64t + 80 = 0

   t2 - 4t - 5 = 0

   (t - 5)(t + 1) = 0

 

t - 5 = 0

t = 5

 

t + 1 = 0

t = -1. Can't be an answer.

 

Explanation: