Tracy and eric are timing how fast marbles roll down an inclined plane. they plan to do this 5 times, and then take the average time for their results. what would be best way to improve the accuracy of their data?

a. include marbles of three different colors
b. include the average of 20 trials down the inclined plane
c. use marbles of ten densities
d. use toy cars instead of marbles

Asled is being held at rest on a slope that makes an angle θ with the horizontal. after the sled is released, it slidesa distance d1 down the slope and then covers the distance d2 alongthe horizontal terrain before stopping. find the coefficient ofkinetic friction μk between the sled and the ground, assumingthat it is constant throughout the trip. find the coefficient of kinetic frictionμk. express your answer in terms of someor all of the variables d1, d2, and θ.