Acceleration physics
posted by Durga .
1. A sprinter finishes the race with a velocity of 8.9 m/s. the sprinter accelerated to a stop at a rate of 2.7 m/s2. how long did it take the sprinter to come to a stop?
2. A cycllist starts from rest & reaches a velocity of 18 m/s southwest in 3.8 seconds. what was the cyclists acceleration?
3. a UFO is flying at a velocity of 45 m/s (E). if 5.9 seconds later it's velocity was 35 m/s (W) what was its acceleration? what assumption did you make?
4. a motorcycle & rider start from rest and reach a velocity of 50 km/h (E) in 2.7 seconds. what was the acceleration of the motorcycle in m/s2?
My answers
1. I don't get how to do it
2. 4.73 m/s2 (SW)
3. 1.69 m/s2 EW
4. 19.2 m/s2
I'm not sure i did these correctly so please help

#1
Keep track of the units. We want time, which is (m/s) / (m/s^2)
SO, divide the change in velocity by the acceleration used:
8.9 m/s divided by 2.7 m/s^2 = 3.30 s
#2 ok
#3
The velocity change by 80 m/s in the W direction. This change took 5.9 seconds, so assuming constant acceleration, we have
80/5.9 = 13.56 m/s W
#4 the acceleration is
50/2.7 km/hr/s = 18.518 km/hr/s
But 1 km/hr = 1000/3600 m/s = 0.2777 m/s
So, 18.518 km/hr/s = 5.14 m/s^2 
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