1.6 Momentum (3)
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1.
A student hits a tennis ball with a racket. Define impulse in terms of force and time. Explain the relationship between impulse, force, and the time over which the force acts.
Definition of Impulse: Impulse is defined as the product of the force applied and the time interval over which the force acts. Mathematically, this is expressed as Impulse = F Δt.
Relationship between Impulse, Force, and Time: Impulse is equal to the change in momentum of an object. Therefore, impulse is directly proportional to the force applied and the time over which the force acts. This means that:
- If the force is greater, the impulse will be greater.
- If the time over which the force acts is longer, the impulse will be greater.
- The impulse is the same regardless of the force applied, as long as the time of impact is the same. This is why using a larger racket (increasing the time of impact) reduces the force felt by the ball.
2.
Describe, in terms of momentum and time, what is meant by the term 'resultant force'. Include the relevant equation.
Concept: Resultant force is defined as the change in momentum of an object per unit time. Momentum (p) is given by the product of mass (m) and velocity (v): p = mv. Therefore, a change in momentum (Δp) is a change in mass * velocity. The change in momentum occurs over a period of time (Δt).
Equation: The equation relating resultant force (F), change in momentum (Δp), and change in time (Δt) is: F = Δp / Δt
Answer: Resultant force is the change in momentum of an object per unit time. It is defined as F = Δp / Δt, where Δp is the change in momentum and Δt is the time interval over which the change occurs.
3.
A 2.0 kg block is moving on a frictionless horizontal surface with a velocity of 3.0 m/s to the right. It collides with a stationary 3.0 kg block. If the collision is perfectly inelastic, calculate the velocity of the combined blocks immediately after the collision.
Solution:
We can use the principle of conservation of momentum. The initial momentum of the system is due to the moving block only. The final momentum is due to the combined mass moving at a final velocity.
Initial momentum (pi) = m1 * v1 = 2.0 kg * 3.0 m/s = 6.0 kg m/s (to the right)
Final momentum (pf) = (m1 + m2) * vf = (2.0 kg + 3.0 kg) * vf = 5.0 kg * vf
Since momentum is conserved, pi = pf. Therefore:
6.0 kg m/s = 5.0 kg * vf
vf = 6.0 kg m/s / 5.0 kg = 1.2 m/s (to the right)
Therefore, the velocity of the combined blocks immediately after the collision is 1.2 m/s to the right.