Download Momentum Problem Solving Skills (Impulse Practice)

Momentum Problem Solving Skills
For problems involving impulse-change of momentum:
1. Draw an accurate diagram locating all of the forces acting on the system.
2. If a net external force acts on the object(s) then the momentum of the system will change.
Determine the magnitude and direction of the net force.
3. Apply the impulse-momentum equation taking note that force and velocity are vectors
and that direction of the vector plays an important part in the solution.
For problems involving no exernal force acting on the system:
1. Use the law of conservation of momentum to solve the problem. Take note that
momentum is a vector quantity and must be considered in the solution.
For problems involving graphical integration:
1. Determine the area under the curve by geometry if it is a simple geometrical shape such
as a rectangle, triangle or trapezoid,
2. If it is not a simple shape put it into a grid and determine the sum of the partial and
complete blocks that lie under the curve.
3. Determine the magnitude of the impulse represented by one block.
4. Determine the magnitude of the total impulse by multiplying the impulse represented by
one block by the total number of blocks found in step 2.
5. Use the impulse-momentum equation and solve the problem.
For problems involving perfectly elastic and completely inelastic collisions:
1. Determine which type of collision is described by the problem.
2. If the collision is completely inelastic and the objects stick together, use the law of
conservation of momentum to solve the problem.
3. If the collision is perfectly elastic, use both conservation of momentum and conservation
of mechanical energy. Each law produces an algebraic equation with two unknowns. The
final velocity of each object can be determined by applying standard algebraic
techniques.
Practice
1. A 100kg car traveling at 22 m/s (about 50mph) strikes a concrete bridge support and
comes to a complete halt in 0.50 seconds.
a) Determine the magnitude of the average force acting on the car.
b) Suppose the bridge support had been surrounded by a barrier that contained
material which is gradually crushed during impact so that the stopping time was
increased to 3.0 s. What would have been the magnitude of the average force?
2. The graph below represents the net force acting on a 2.0 kg toy car during a time interval
of 5.0 s
a) Use graphical integration to determine the magnitude of the impulse delivered to
the car.
b) The car was initially at rest. Determine the car’s speed after 5 s.