An object of mass 100g projected vertically upwards from the ground level has a velocity of 20ms\(^{-1}\) at a height of 10m. Calculate its initial kinetic energy at the ground level.[g = 10ms\(^{-2}\), neglect air resistance]
10 J
20 J
30 J
50 J
Explanation
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Discussions (35)
This explanation is not clear..and seems partly incorrect...
...it is sopposed to be somthing like this..
Using..
2 2
V = U - 2gh..
Where V= 20,g=10,h=10
.^.substituting..we have
2
400=U -200
.^.U^2=400+200=600m/s
2
K.E = 1/2mV
Where V^2=U^2=600m/s
Converting to SI unit,
m=(100/1000)kg or O.1kg
.^. K.E=1/2x 1/10 x 600
=30J..
This explanation is not clear..and seems partly incorrect...
...it is sopposed to be somthing like this..
Using..
V^2 = U^2 - 2gh..
Where V= 20,g=10,h=10
.^.substituting..we have
400=U^2 -200
.^.U^2=400+200=600m/s
2
K.E = 1/2mV
Where V^2=U^2=600m/s
Converting to SI unit,
m=(100/1000)kg or O.1kg
.^. K.E=1/2x 1/10 x 600
=30J..
To find the initial kinetic energy, we need to calculate the initial velocity (v0) at the ground level.
Given:
Mass (m) = 100 g = 0.1 kg
Height (h) = 10 m
Velocity (v) at 10 m = 20 m/s
Acceleration due to gravity (g) = 10 m/s²
Using the equation v² = v0² - 2gh, we can find the initial velocity (v0):
20² = v0² - 2 × 10 × 10
400 = v0² - 200
v0² = 600
v0 = √600 ≈ 24.49 m/s
Initial kinetic energy (KE0) = 1/2 × m × v0²
= 1/2 × 0.1 × 600
= 30 J
The correct answer is:
C) 30J
Funny how I also used the usual formula and still got the same answer
PE+KE
mgh +¹/2mv²
0.1×10×10 + ¹/2×0.1×20²
10+20 =30J.
the questions says K.E at ground level. please don't be confused
K.E at ground level= P.E
I MEAN
K.E= P.E = Mgh
0.1×10×10 = 10J
A
