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January 25, 2015

January 25, 2015

Posted by **philip** on Friday, September 23, 2011 at 12:17pm.

A car starts from rest and reaches a velocity of 40m/s in 1minutes..(a)what is its acceleration?(b) If its acceleration remains constant,what will its velocity be in 15 minutes?

The brakes of a certain car can produce an acceleration of 6m/s2.(a)how long does it take the car to come to a stop from a velocity of 30m/s?(b) how far does the car travel during the time the brakes are applied?

A train is uniformly decelerated at 2.5 m/s2 during a 2s period.how far does it travel before coming to a full stop?

A cyclist travelling uniformly at 30m/s sees a post 300m away and suddenly applies his brakes.If the bike stops in 4.8s,determine whether the cyclist hits the post.

A boy increases speed from 1.2m/s to 2.4m/s in 6s,how far does the boy travel?

- physics -
**Henry**, Sunday, September 25, 2011 at 6:56pm1 hr = 3600s.

Vf = Vo + at,

Vf = 0 + 0.98*3600 = 3528m/s.

a. a = (Vf - Vo) / t,

a = (40 - 0) / 60s = 0.67m/s^2.

b. t = 15 min. * 60s/min = 900s.

Vf = Vo + at,

Vf = = 0 + 0.667 * 900 = 600m/s.

a. t = (Vf - Vo) / a,

t = (0 - 30) / -6 = 5s.

b. d = (Vf^2 - Vo^2) / 2a,

d = (0 - (30)^2) / -12 = 75m.

Vf = Vo + at,

Vo = Vf - at,

Vo = 0 - (-2.5)*2 = 5m/s.

d = (Vf^2 - Vo^2) / 2a,

d = (0 - (5)^2) / -5 = 5m.

- physics -
**Henry**, Sunday, September 25, 2011 at 7:03pmCorrection: Disregard the 1st 3 lines,

and start at "a".

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