Motion and Forces [High School]

AI Thread Summary
Mariana strikes a tennis ball moving at 35 km/h, returning it at 55 km/h, resulting in a calculated acceleration of -333 m/s² and a force of 20N acting on the ball in the backward direction. The discussion highlights confusion regarding the force applied by the ball on the racquet, with participants noting the relevance of Newton's third law. It is suggested that the force exerted by the ball on the racquet is equal in magnitude and opposite in direction, leading to a conclusion that the force is 20N forward. Clarification on the uniform motion concept is sought, emphasizing the need for understanding forces in non-uniform scenarios. The thread concludes with a focus on applying Newton's laws to solve the problem effectively.
Liam C
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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.
 
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Liam C said:
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?
 
PeroK said:
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.
 
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