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CBSE Class 9 Answered

a body of mass 5 kg is thrown vertically upward with a velocity of 20 metre per second find

1- initial kinetic energy

2-kinetic energy and potential energy after 1 second( given g  =10 /s^2)

Asked by karanbora625 | 26 Oct, 2019, 06:44: PM
Expert Answer
m = 5 kg
u = 20 m/s (Initial velocity)
Initial kinetic energy, 
K.E. = 1/2 mv2 
K.E = 1/2 × (5) (20)2 
K.E. = 1000 J 
 
Thus, initial kinetic energy is 1000 J 
 
Now, the speed with which the body is thrown is 20 m/s 
Thus, height reached by body after 1 s is, 
 
h = ut + 0.5 gt2 
h = (20) (1) +0.5 (-10) (1) ... (negative sign for g indicates that the body is thrown against the gravity)
h = 15 m 
 
P.E. = mgh = 5 × 10 × 15 = 750 J
The initial kinetic energy = total energy required to throw the body
Thus, 
Kinetic energy after 1 s is, 
T.E = P.E. + K.E. (after 1 s)
1000 J = 750 J + K.E. (after 1 s) 
K.E (after 1 s) = 1000 - 750 = 250 J 
 
 
 
Thus, after 1 s, the kinetic energy will get completely converted 
Answered by Shiwani Sawant | 28 Oct, 2019, 06:36: PM
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