Conceptual Physics Momentum Exam

Conceptual Physics Momentum Exam Momentum - Answer-The product of the mass of an object and its velocity. Momentum = mass × velocity Momentum is... - Answer-a property of moving things. By momentum we mean... - Answer-Inertia in motion. Momentum in shorthand: - Answer-Momentum→Ρ =mv When direction is not an important factor, we can say: - Answer-Momentum = mass × velocity What is especially important when dealing with momentum? - Answer-Timing The quantity force × time interval is called: - Answer-Impulse Impulse - Answer-The product of the force acting on an object and the time during which it acts. Relationship of impulse and momentum - Answer-Impulse is equal to the change in momentum of the object that the impulse acts upon. In symbol notation, Ft = I Law of conservation of momentum - Answer-In the absence of an external force, the momentum of a system remains unchanged. Hence, the momentum before an event involving only internal forces is equal to the momentum after the event: *mv (before event) = mv (after event) Elastic collision - Answer-A collision in which colliding objects rebound without lasting deformation or the generation of heat. Inelastic collision - Answer-A collision in which the colliding objects become distorted, generate heat, and possibly stick together. Impulse = - Answer-Force x time The delta symbol: ∆ - Answer-a letter in the Greek alphabet used to denote "change in" or "difference in" FT= I Ft = I - Answer-This relationship is derived by rearranging Newton's second law to make the time factor more evident. If we equate the formula for acceleration, a =F/m, with what acceleration actually is, a = ∆v/∆t, we get F/m = ∆v/∆t. From this we derive F∆t = ∆Ρ. Calling ∆t simply t, the time interval, Ft = ∆Ρ. Case 1: Increasing Momentum - Answer-To increase the momentum of an object, it makes sense to apply the greatest force possible for as long as possible. The forces involved in impulses usually vary from instant to instant. When we speak of forces in this chapter, we mean the average force. Case 2: Decreasing Momentum - Answer-It takes the same impulse to decrease your momentum to zero. The same impulse does not mean the same amount of force or the same amount of time; rather it means the same product of force and time. By hitting a haystack instead of a wall, you extend the time during which your momentum is brought to zero. A longer time interval reduces the force and decreases the resulting deceleration. For example, if the time interval is extended 100 times, the force is reduced to a hundredth. Whenever we wish the force to be small, we extend the time of contact. Hence, the padded dashboards and airbags in motor vehicles. If the change in momentum occurs over a long time, the hitting force is small. - Answer-I → FΤ If the change in momentum occurs over a short time, the hitting force is large. - AnswerI = Ft Case 3: Decreasing Momentum over a Short Time - Answer-(a) When a boxer moves away (rides with the punch), he extends the time and diminishes the force. FT = change in momentum (b) If the boxer moves into the glove, the time is reduced and he must withstand a greater force. Ft = change in momentum In both cases, the impulse provided by the boxer's jaw reduces the momentum of the punch. (a) FT = change in momentum (b) Ft = change in momentum - Answer-Remember that, (a) and (b), for an object brought t rest, the impulse is the same, no matter how it is stopped. But, if the time is short, the force will be large. Momentum is conserved for... - Answer-all collision, elastic and inelastic (whenever external forces don't interfere).