Question

If a racket strikes a ball (m = 100 g) with a force of 2000 N for 0.3 s., calculate the velocity the ball has as it leaves the racket, assuming it starts from rest.

v = _____ m/s

6 m/s
60 m/s
600 m/s
6000 m/s

Answer 1

Force can be calculated by the product of mass and the acceleration of the object in motion. Acceleration is the change of velocity per change in time. The expression would be:

F = ma

where
a = Δv/Δt
The object is from rest and time 0. Acceleration would reduce to:
a = v/t

F = m(v/t)
2000 = 100 (v / 0.3)
v = 6 m/s -------> OPTION 1

Answer 2

By impulse definition we have to:

F * Δt = m * Δv

Where,

F: Applied force

Δt: change in time

m: mass

Δv: change in speed

Substituting values we have:

2000 * (0.3 - 0) = (0.1) * (v - 0)

From here, we clear the speed.

We have then:

2000 * 0.3 = 0.1v

v = (2000 * 0.3) / (0.1)

v = 6000 m / s

Answer:

the velocity the ball has as it leaves the racket, assuming it starts from rest is:

v = 6000 m / s