4. Dynamics  9702 Physics Summary Notes
4.1 Newton’s Laws of Motion
·
First law: if a body is at rest it remains at rest or if it is in
motion it moves with a uniform
velocity until it is acted on by resultant force or torque
·
Second law: the rate
of change of momentum of a body is proportional to the resultant force
and occurs in the direction of force; F=ma
·
Third law: if a body A exerts a force on a body B, then body B
exerts an equal but
opposite force on body A, forming an actionreaction pair
4.2 Mass and Weight
Mass

Weight

·
Measured in kilograms
·
Scalar quantity
·
Constant throughout the universe

·
Measured in Newtons
·
Vector quantity
·
Not constant
·
W=mg

·
Mass: is a measure of the amount of matter in a body, & is the
property of a body which resists
change in motion.
·
Weight: is the force
of gravitational attraction (exerted by the Earth) on a body.
4.3 Momentum
· Linear momentum: product of mass and
velocity
p = mv
· Force: rate of change of momentum
F = (mv  mu) / t
· Principle of conservation of linear momentum:
when bodies in a system interact, total momentum remains constant provided no
external force acts on the system.
m_{A}u_{A}
+ m_{B}u_{B} = m_{A}v_{A} + m_{B}v_{B}
4.4 Elastic Collisions
· Total
momentum conserved
· Total kinetic energy is conserved
Example:
Two identical spheres collide elastically. Initially, X is moving with speed v and Y is stationary. What happens
after the collision?
X stops and Y moves with speed v
Relative velocity before collision =
Relative velocity after collision
u_{A}
 u_{B} = v_{B}  v_{A}
4.5 Inelastic Collisions
relative speed of approach > relative speed of separation
o Total
momentum is conserved
· Perfectly inelastic collision:
only momentum is conserved, and the particles stick together after collision (i.e. move with the
same velocity)
· In
inelastic collisions, total energy is conserved but
Ek may
be converted into other forms of energy e.g. heat
i need help in this question
ReplyDeleteQ: A stationary nucleus of mass 220u undergoes radioactive decay to produce a nucleus D of mass 216u and alpha particle of mass 4u
the initial kinetic energy of the alpha particle is 1*10^12(one times ten to the power of negative twelve)
A) (i)state the law of conservation of linear momentum
(ii) explain why the initial velocities of the nucleus D and the alpha particle must be in opposite directions
B)(i) show that the initial speed of alpha particle in 1.7*10^7 m/s
(ii)calculate the initial speed of nucleus D
c) the range in air of the emitted alpha particle is 4.5 cm
calculate the average deceleration of the alpha particle as it is stopped by the air
A stationary nucleus of mass 220u undergoes radioactive decay to produce a nucleus D of
ReplyDeletemass 216u and an αparticle of mass 4u
The initial kinetic energy of the αparticle is 1.0 × 10^–12 J.
(ii) Explain why the initial velocities of the nucleus D and the αparticle must be in
opposite directions.
(b) (i) Show that the initial speed of the αparticle is 1.7 × 10^7 m/s.
(ii) Calculate the initial speed of nucleus D.
(c)The range in air of the emitted αparticle is 4.5 cm.
Calculate the average deceleration of the αparticle as it is stopped by the air.
Check solution 1098 at
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