A hockey player uses a 400- gram stick to apply 50 newtons of force to a 170-gram puck, causing a momentum of change 5kg x m/s.
1 answer:
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Solution :
Given :
Mass of the baseball, m = 200 g
Velocity of the baseball, u = -30 m/s
Mass of the baseball after struck by the bat, M = 900 g
Velocity of the baseball after struck by the bat, v = 47 m/s
According to the conservation of momentum,
(900 x 47) + (200 x -30) = (900 x ) + (200 x
)
36300 = (900 x ) + (200 x
)
..............(i)
The mathematical expression for the conservation of kinetic energy is
................(ii)
Substituting (i) in (ii)
Solving the equation, we get
The negative velocity is neglected.
Therefore, substituting 96 m/s for in (i), we get
= 19
Thus, only impulse of importance is used to find final velocity.
Momentum is conserved if and only if sum of all forces which are exserted on system equals zero. In our situation there are only internal forces, so by Newton's third law their vector sum is 0.
So .
Kinetic energy of system at first: . After:
. The secret is that other energy is in work of deformation forces (they in turn heat a bullet and a block).
Answer is A)