Motion and Forces [High School]

[Liam C]

Homework Statement

Mariana is volleying with Old Man Miller and returns one of his feeble tennis serves. He serves the ball such that it is moving at a speed of 35km/h [Forward] when she strikes the 0.060kg ball and sends it back over the net at a velocity of 55km/h[Backward].

a) If the ball spends 0.075 seconds in contact with the racquet determine the force acting on the ball.
b) What was the force applied by the ball on the racquet during the stroke?

Homework Equations

Fnet = ma

The Attempt at a Solution

a)
I’m assuming it’s talking about Mariana’s stroke:
V1 = 35/3.6 m/s = 9.72m/s
V2 = -55/3.6 m/s = -15.28m/s
t = 0.075s
m = 0.060kg

a = V2 - V1 / t
a = -15.28 - 9.72 / 0.075
a = -333m/s^2
ΣF = ma
ΣF = (0.060)(-333)
ΣF = -20N
∴ The force acting on the ball was 20N [Backward]
Is it asking for a net force and is that what I provided?

b)
I have no idea how to find the force applied by the ball. If it is horizontal motion then isn’t the motion uniform? How do I find the force of an object moving uniformly? I’d like some help approaching this question.

 

[PeroK]

b)
I have no idea how to find the force applied by the ball. If it is horizontal motion then isn’t the motion uniform? How do I find the force of an object moving uniformly? I’d like some help approaching this question.

How many of Netwon's laws do you know?

 

[Liam C]

How many of Netwon's laws do you know?

My teacher taught us the first two and gave us a homework sheet with a bunch questions like this for March break.

 

[PeroK]

My teacher taught us the first two and gave us a homework sheet with a bunch questions like this for March break.

Interesting. It's Netwon's third law that is useful here:

https://www.khanacademy.org/science...ns-laws-of-motion/a/what-is-Newtons-third-law

 

[Liam C]

Interesting. It's Netwon's third law that is useful here:

https://www.khanacademy.org/science...ns-laws-of-motion/a/what-is-Newtons-third-law

Oh thank you.

 

[Liam C]

Interesting. It's Netwon's third law that is useful here:

https://www.khanacademy.org/science...ns-laws-of-motion/a/what-is-Newtons-third-law

So would the answer to b) be 20N [forward] ?
If you separate the system of the ball from the system of the racquet it seems to me that the ball would be propelled forward by the same force it hit the racquet with.