Newtons 3 rd law and momentum. S I R I S A A C N E WTON (1647 - 1727). Newton worked in the 1600s. He talked about momentum before he talked about force but, maybe because momentum is hard to conceptualise, we learn Newton’s Laws as statements about force.
(1647 - 1727)
momentum = mass x velocity
p = mv
(kgms-1)=(kg) x (ms-1)
= 1500 x 21
= 31 500 kgms-1
Question:On icy winter roads a 1500kg car travelling at 21m/s collides with a 1800kg van going 15m/s in the opposite direction. The two vehicles lock together (1D collision) and move off with a new speed v. Find v.
Draw a diagram
Find the initial momentum of each and add (considering direction)
Find the combined mass and multiply by new v
Equate and solve
Ptruck = 1800 x 15
Pcar = -1500 x 21
Ptotal = 4 500 kgms-1
Mass = 3300kg
4 500 = 3300 x v
V = 4500/3300
= 1.4 ms-1 (in direction of car)
change = final vector – initial vector
An ice hockey puck of mass 0.8kg moving at 3.5ms-1 hits the side of a second puck initially at rest. The mass of the second puck is 0.70kg.
After the collision the 0.8kg puck moves off at 2.8ms-1 at right angles to its original direction.
Find the velocity of the second puck immediately after the collision
Final – initial = Final + opposite
3.6kgm/s on an angle of 37o
“ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE”
“IF A BODY A EXERTS A FORCE ON BODY B, THEN B EXERTS AN EQUAL AND OPPOSITELY DIRECTED FORCE ON A”
I’LL PULL HIM
WELL, ACTION FORCE AND REACTION FORCE ARE ALWAYS EQUAL AND OPPOSITE!!
WELL ACTION AND REACTION ARE ALWAYS EQUAL AND OPPOSITE!!
SO WHY DOES THE GIRL MOVE FASTER?
The 2 forces act for the same length of time
The 2 forces act on different bodies
The 2 forces are in opposite directions
The 2 forces are the same size
The 2 forces act along the same line
Both forces are of the same type
THE CLUB EXERTS A FORCE F ON THE BALL
THE BALL EXERTS A N EQUAL AND OPPOSITE FORCE F ON THE CLUB