Ball rolls 6cm in one second. 6cm x 40 sec = 240cm
The maximum speed is 0.55 m/s
Explanation:
For an object in uniform circular motion, the force of friction between the object and the ground provides the centripetal force required to keep the body in motion. Therefore we can write:

where the term on the left is the frictional force and the term on the right is the centripetal force, and where
is the coefficient of static friction
m is the mass of the body
g is the gravitational acceleration
v is the speed of the body
r is the radius of the circular path
In this problem, we have:

r = 0.102 m

Substituting and re-arranging, we find the maximum speed v at which the salt shaker can rotate:

Learn more about circular motion:
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Answer:
a. Photogates placed at the beginning, end, and at various locations along the track that the car travels on.
b. A meterstick to measure the distance of the track that the car travels on.
Explanation:
Physics can be defined as the field or branch of science that typically deals with nature and properties of matter, motion and energy with respect to space, force and time.
In this scenario, a student is provided with a battery-powered toy car that the manufacturer claims will always operate at a constant speed. The student must design an experiment in order to test the validity of the claim.
Therefore, to test the validity of the claim, the student should use the following measuring tools;
a. Photogates placed at the beginning, end, and at various locations along the track that the car travels on. This device is typically used to measure time with respect to the rate of change of the interruption or block of an infra-red beam.
b. A meterstick to measure the distance of the track that the car travels on.
Hence, with these two devices the student can effectively measure or determine the validity of the claim.
Answer: 
Explanation:
Given
Power 
Distance from the light source 
Intensity is given by

Inserting values

Answer:
To have a positive job, the two vectors must have the same direction
Explanation:
Work is a scalar defined as the scalar product of two vectors, the froce and the displacement. To have a positive job, the two vectors must have
collinear and that their arrows point in the same direction.
You can also appreciate this from the work equation
W = F. r
bold indicate vector
W = F r cos θ
With θ the angle between force and displacement