physics question on speed acceleration and velocitty?

2015-08-29 1:14 pm

A Car start travels from 0 m/s.It increase velocity up to 30 m/s(uniform acceleration) in 10 seconds.then again decreese velocity to 0(uniform deceleration) in 15 sec. And rest another 15 sec. then again travels and increase velocity to 50m/s (uniform acceleration) in 10 sec.

1)calculate the whole length of whole journey (10 marks)

2) calculate the uniform acceleration of each part(15 marks)

回答 (1)

micatkie

2015-08-29 2:41 pm

(1)
Part 1: From 0 m/s to 30 m/s in 10 seconds
s = [(vₒ + v)/2] t
s = [(0 + 30)/2] × 10 = 150 m

Part 2: From 30 m/s to 0 m/s in 15 seconds
s = [(vₒ + v)/2] t
s = [(30 + 0)/2] × 15 = 225 m

Part 3: Rest 15 seconds
s = 0

Part 4: From 0 m/s to 50 m/s in 10 seconds.
s = [(vₒ + v)/2] t
s = [(0 + 50)/2] × 10 = 250 m

Whole length of the journey = 150 + 225 + 0 + 250 = 625 m

(2)
Part 1: From 0 m/s to 30 m/s in 10 seconds
v = vₒ + at
30 = 0 + a(10)
Acceleration, a = 3 m/s²

Part 2: From 30 m/s to 0 m/s in 15 seconds
v = vₒ + at
0 = 30 + a(15)
Acceleration, a = ‒2 m/s²

Part 3: Rest 15 seconds
Acceleration, a = 0

Part 4: From 0 m/s to 50 m/s in 10 seconds.
v = vₒ + at
50 = 0 + a(10)
Acceleration, a = 5 m/s²

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