If you drive for 20 miles to the right for 1/2 an hour, stop for a coffee break

Question

If you drive for 20 miles to the right for 1/2 an hour, stop for a coffee break for one hour, and drive 42 miles to the left for 3/4 of an hour. (Assume the car is moving at constant speed and it is initially already moving and doesn't come to rest at the end)

a. Find the average speed during the 1st Stage, S1, 2nd Stage, S2 and the total average speed S tot.

b. Find the average velocity during the 1st Stage, V1, 2nd Stage, V2 and total average average velocity V tot.

c. Find the average acceleration during 1st stage, A1, 2nd Stage, A2 and total average acceleration A tot.

d. Draw graphs of x vs. t, v vs, t, s vs. t and a vs. t. On the graph of x vs t AND v vs t show the geometrical meaning of V1, V2 and V tot. On v vs t show the meaning of A1, A2 and A tot. On s vs t show S1 avg S2 avg and S tot. on a graph of a vs t show A1, A2 and A tot!

Explanation / Answer

If you drive for 20 miles to the right for 1/2 an hour, stop for a coffee break for one hour, and drive 42 miles to the left for 3/4 of an hour. (Assume the car is moving at constant speed and it is initially already moving and doesn't come to rest at the end)

a. the average speed during

the 1st Stage, S1 = 20/0.5 = 40 mph

, 2nd Stage, = 42/0.75 = 56 mph

S2 and the total average speed S tot. = total distance travelled/total time taken

S = (20+42) / (0.5+1+0.75) = 27.55 mph

b. the average velocity during

the 1st Stage, V1= 20/0.5= 40 mph

2nd Stage, V2 = 42/0.75= 56 mph

and total average average velocity V tot. = total dispalceement/total time taken

V tot. = (42-20)/(0.5+1+0.75) = 9.77 mph

c. the average acceleration during

the car is moving at constant speed and it is initially already moving and doesn't come to rest at the end)

then acceleration would be zero

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