Question

a 15kg rock falls from the top of a building 8.0 high. Find its PE and KE
a.when at rest at the top of the building
b. halfway down the ground
c. when it reaches the ground
d.speed when it reaches the ground

Answer 1

a) when at rest
PE=mgh
h=8m
mgh = (15kg)(9.81m/s^2)(8m)=1177.2 J

KE = (1/2)*m*v^2
there is no velocity, v=0
so KE = 0J

b)
PE=(15kg)*(9.81m/s^2)(8/2m) = ?J
There is no KE while it's falling
KE = 0J

c) PE= m*g*h = (15)(9.81)(0) =0J

KE =(1/2)m*v^2
where v=sqrt(2*g*h)
= (2*9.81*8) = 12.53 m/s

KE = (1/2)*(15)*(156.96)^2 = ? J

d) speed when it reaches the ground:
v=12.53 m/s


To check:

PE_initial + KE_initial = PE_final + KE_final



1177.2J + 0J = 0J + 1177.2J

Answer 2

for part c), I made a typo:

KE = (1/2)*(15)*(12.53)^2 = 1177.2J

Answer 3

where did u get 12.53m/s

Answer 4

Taena niyo ayos para sa activity ko to sa school eh

Answer 5

2 joints parang mafia

Answer 6

Control your temper so dont be angry

Answer 7

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Answer 8

mga kumukuha ng sagot diyan mga grade 11 hule kayoo

Answer 9

grade 12 pala nakopo hulee

Answer 10

ang gulo ng explanation pero okay lang haha