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Answer the following regarding Momentum Change and Force:

A) A top-class tennis player can serve the ball, of mass 57 g, at an initial horizontal speed of 50 m/s. The ball remains in contact with the racket for 0.05 s. Calculate the average force exerted on the ball during the serve.

B) A motor car of mass 3000 kg moving with 72 km h-1 made to reduce its speed to 18 km h^-1, in 40 s, by applying brakes. Find the resistive force.

Respuesta :

Eduard22sly

A. The average force exerted on the ball during the serve is 57 N

B. The resistive force, given the data is -1125 N

A. How to determine the average force

  • Mass (m) = 57 g = 57 / 1000 = 0.057 Kg
  • Initial velocity (u) = 50 m/s
  • Time (t) = 0.05 s
  • Acceleration (a) = u / t = 50 / 0.05 = 1000 m/s²
  • Force (F) = ?

F = ma

F = 0.057 × 1000

F = 57 N

B. How to determine the resistive force

  • Mass (m) = 3000 Kg
  • Initial velocity (u) = 72 Km/h = 72 / 3.6 = 20 m/s
  • Final velocity (v) = 18 Km/h = 18 / 3.6 = 5 m/s
  • Time (t) = 40 s
  • Force (F) = ?

F = m(v – u) / t

F = 3000(5 – 20) / 40

F = -1125 N

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