Considered Formula; Motion Under Gravity
i)v=u+gt Where u→Initial velocity,v→Final velocitya→Acceleration due to gravityt→Time ii)s=ut+12gt2 Where s→Distance traveled,u→Initial velocity,a→Acceleration due to gravityt→Time iii)v2=u2+2gs Where u→Initial velocity,v→Final velocity,a→Acceleration due to gravity,s→Distance traveledExample 1
A stone of mass 2kg is released from a height of 20m above the ground. Find
a)
Velocity reached just before hit the ground
b) Time taken to reach the ground
Solution
Data given
Distance (s) = 20 m
Accelaration due to gravity (g) = 10 m/s2
a)
Final velocity (v) = ?
v2=2gs⇒Initial velocity (u)=0 v=√2gs =√2(10)(20) =√400 =20 m/s
The final velocity = 20 m/s
b)
Time (t) = ?
v=gt 20=10t 10t10=2010 t=2 sec
The time taken to reach the ground = 2seconds
Example 2
A stone is thrown vertically upward from the ground with a velocity of 30 m/s. find
a)
Maximum height reached
b) Time taken to reach the maximum height
c) Time taken to reach the ground again
d) The velocity reached half-way to the maximum height
Solution
Data given
Initial velocity (u) = 30 m/s
Final velocity (v) = 0 m/s
Accelaration due to gravity (g) = 10 m/s2
a)
Distance (s) = ?
For upward motion, g = -10 m/s2
v2=u2+2gs 02=302+2(−10)s 0=900−20s 20s=900 20s20=90020 s=45 m
The maximum height reached = 45 m
b)
Time taken to reach maximum height (t1) = ?
v=u+at 0=30+10t1 10t1=0−30 10t1=−30 10t110=−3010 t1=3 sec
The time taken to reach maximum height = 3 seconds
c)
Time taken to reach ground again (t2) = ?
t2=2t1 =2×3 =6 sec
The time taken to reach ground again = 6 seconds
d)
Final velocity (v) = ?
Time (t)=(32)=1.5 sec
v=u+at =30+(−10×1.5) =30−15 =15 m/s2
The velocity reached half-way to the maximum height = 15 m/s
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