 ### Momentum

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 1. Define momentum. Answer Momentum is defined as being the product of the mass of an object and it’s velocity, or the ‘quantity of motion’.
 2. Is momentum a vector or a scalar quantity? Answer Vector You must provide a direction as well in your final answer.
 3. A trolley X of mass 6kg has a velocity of 4ms-1 east. Calculate it’s momentum. Answer p = mv p = 6(4) p = 24kg.m.s-1 east
 4. Calculate the change in momentum of a 3kg trolley if the velocity of the trolley increased from 5ms-1 east to 7ms-1 east. Answer Δp = m(vf - vi) Δp = 3(7 - 5) Δp = 6kg.m.s-1 east
 5. Calculate the change in momentum of a 5kg trolley if the velocity of the trolley changed from 8ms-1 east to 12ms-1 west. Answer Choose final direction as positive Thus west is positive, and east is negative. Δp = m(vf - vi) Δp = 5(12 - (-8)) Δp = 5(20) Δp = 100 kg.m.s-1 Since answer is positive, Δp is 100 kg.m.s-1 west
 6. A force of 4N acts west on a trolley for 3s. Calculate the impulse exerted on the trolley. Answer Δp is also called IMPULSE Δp can also be calculated from: Δp = FΔt Δp = 4(3) Δp = 12N.s west
 7. The velocity of a 2kg trolley changed from 4ms-1 east to 7ms-1 east over a period of 10s. Calculate the force that must have been used. Answer Since Δp = m(vf - vi) and Δp = FΔt FΔt = m(vf - vi) F(10) = 2(7 - 4) F = 0,6 N east.
 8. An arrow of mass 250g strikes a wooden block with a velocity of 80ms-1 east and is brought to a halt in 0,8s. Calculate the stopping force. Answer m = 0,25kg vf = 0 (stopped) positive = east FΔt = m(vf - vi) F(0,8) = 0,25(0 - 80) F(0,8) = -20 F = -25N F = 25N west (the negative sign means west)
 9. The rate of change of momentum is equivalent to : A. impulse B. force C. energy D. power Answer B. force FΔt = Δp F = Δp/Δt The right hand side is called "rate of change of momentum" and it is equal to force (resultant).
 10. A body of mass m strikes a wall perpendicularly with a speed of v and bounces directly back with no change in its speed. The change in its momentum would be: A. zero B. mv C. 2mv D. 2v Answer C. 2mv two directions = two signs Let final velocity = v Then initial velocity = -v Δp = m(vf - vi) Δp = m(v -(-v)) Δp = m(v + v) Δp = m(2v) Δp = 2mv