Answer:

Explanation:
Let say the ball is projected at an angle with horizontal
So here two components of the velocity of the ball is given as


now the displacement in x direction is given as


in y direction it is given as


now from above two equations




The speed of the rock at 20 m is 34.3 m/s
Explanation:
We can solve this problem by using the law of conservation of energy: the mechanical energy of the rock, sum of its potential energy + its kinetic energy) must be conserved in absence of air resistance. So we can write:
where
:
is the initial potential energy
is the initial kinetic energy
is the final potential energy
is the final kinetic energy
The equation can also be rewritten as follows:
where:
m = 100 kg is the mass of the rock
is the acceleration of gravity
is the initial height
u = 0 is the initial speed (the rock starts at rest)
is the final height of the rock
v is the final speed when h = 20 m
And solving for v, we find:

Learn more about kinetic energy and potential energy here:
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Answer:
T = 1010 degree Celsius
Explanation:
mass of ball (Mb) = 100 g
mass of water (Mw) = 400 g
temp of water = 0 degree
specific heat of platinum (C) = 0.04 cal/g degree celsius
we can calculate the temperature of the furnace from the equation before
Mb x C x (temp of furnace (T) - equilibrium temp) = Mw x (equilibrium temp - temp of furnace)
100 x 0.04 x ( T - 10) = 400 x (10 - 0)
4 (T - 10) = 4000
T - 10 = 1000
T = 1010 degree Celsius
10 kilograms of mass weighs 98.1 newtons on Earth,
16.2 newtons on the Moon, 37.1 newtons on Mars,
and other weights in other places.