Question

A robot standing at the bottom of cliff shoots a ball upwards .The ball reaches max height of 80m in 4s .what is the height of the cliff if it reaches the top of the cliff 7s after the shoot?​

Answer 1

Given:

A robot standing at the bottom of cliff shoots a ball upwards. The ball reaches max height of 80m in 4s .

To find:

What is the height of the cliff if it reaches the top of the cliff 7s after the shoot?​

Solution:

From given, we have,  

The ball reaches max height of 80m in 4s.

we use the formula,

S = 1/2(u + v)t

80 = 1/2(u + 0)4

160 = 4u

u = 40 m/s

Magnitude of acceleration due to gravity,

a = |(v - u) /t|= |(0 - 40)/4| = 10 m/s^2

Based on the given data, we have obtained a = 10 m/s^2

Distance moved from top to cliff be = x

S = ut + (1/2)at^2

x =0 × (7 - 4) + (1/2) × 10 × (7 - 4)^2

x = 0 + 5(9)

x = 45 m

Height of cliff = 80 m - 45 m = 35 m

Therefore, the height of the cliff is 35 m.