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igcse physics notesprinted 36 · PDF 36
124 pagesrevision 46936
printed 36 · PDF 36
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As shown in the next diagram, a ball is moving with a velocity of 0.5 m/s.
Suppose its mass is 10 kg. To calculate momentum, 0.5*10 = 5 kgm/s.
Change in Momentum:
It is the difference between initial and final momentum. Its formula is Δp=
mv-mu where “ Δ” means change, mv is final momentum and mu is
initial momentum.
In the above example, a ball hits the wall and then comes back. Suppose
the ball has mass 4 kg. u (velocity before hitting the wall) = 5 m/s and v
(velocity after hitting the wall) = -3 m/s. Here negative “-” sign is used
because direction is opposite and velocity is a vector quantity so to show
this we use “-” sign.
Applying formula: change in momentum= mv (final momentum) - mu (initial
momentum) = m(v-u) = 4((-3)-(5)) = 32 kgm/s.
Newton’s second Law:
Rate of change of momentum is directly proportional to the force. F=k
(change in momentum/time) where k is a constant (1) hence
F = ((mv-mu)/t) -> F = m((v-u)/t) -> F=ma where “m” is mass and “a” is
acceleration.