A ball flying at a speed of 12 m / s is thrown by a racket hit in the opposite direction at a speed of 18 m / s.

| April 29, 2021 | education

A ball flying at a speed of 12 m / s is thrown by a racket hit in the opposite direction at a speed of 18 m / s. The change in its kinetic energy is 10 J. Find the average impact force if the racket’s action time on the ball is 0.1 s.

V1 = 12 m / s.

V2 = 18 m / s.

ΔEk = 10 J.

t = 0.1 s.

F -?

Let us express the change in the kinetic energy of the ball ΔEk = m * V2 ^ 2/2 – m * V1 ^ 2/2 = m * (V2 ^ 2 – V2 ^ 2) / 2.

Let’s find the mass of the ball by the formula: m = 2 * ΔEk / (V2 ^ 2 – V1 ^ 2).

m = 2 * 10 J / ((18 m / s) ^ 2 – (12 m / s) ^ 2) = 0.11 kg.

Let’s write 2 Newton’s law: F = m * a.

a = (V2 – V1) / t – vector.

a = (V2 + V1) / t, since the speeds are directed in opposite directions.

F = m * (V2 + V1) / t.

F = 0.11 kg * (18 m / s + 12 m / s) / 0.1 s = 33 N.

Answer: the average hitting force of the racket is F = 33 N.



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