IB Physics SL A.2.7 Frictional Force

Practise choosing static or dynamic friction, calculating the normal reaction first and using the frictional force with Newton's laws or kinematics on horizontal and inclined…

Exam points

compare the required friction with the static limit μsN before deciding whether an object slides
use Ff = μdN only during sliding and calculate N from the perpendicular force balance
insert friction with the correct direction in F = ma or an energy and kinematics calculation

[Maximum number: 3]

A student strikes a tennis ball that is initially at rest so that it leaves the racquet at a speed of $64 \mathrm{~m} \mathrm{~s}^{-1}$ . The ball has a mass of 0.058 kg and the contact between the ball and the racquet lasts for 25 ms .

The student models the bounce of the tennis ball to predict the angle $\theta$ at which the ball leaves a surface of clay and a surface of grass.

Figure for Question A.2.7—Frictional force question 1 — IB Physics SL

The model assumes
- during contact with the surface the ball slides.
- the sliding time is the same for both surfaces.
- the sliding frictional force is greater for clay than grass.
- the normal reaction force is the same for both surfaces.
Predict for the student's model, without calculation, whether $\theta$ is greater for a clay surface or for a grass surface.

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A.2.7—Frictional force question 1