7. A helicopter’s speed increases from 25 m/s to 60 m/s in 5 seconds. What is the acceleration of this helicopter?
8. As she climbs a hill, a cyclist slows down from 25 mi/hr to 6 mi/hr in 10 seconds. What is her deceleration?
Acceleration is defined as ( change in velocity / change in time )
Velocity change = Vf - Vo = final velocity - original velocity = 60 - 25 m/s = 35 m/s
Change in time = 5 s
35 m/s / 5 s = 7 m/s^2
2: Same thing here (6 m/hr - 25 m/hr)/ 10s = -19 m/hr / 10 s
Note that m/hr is not in the same units as ' s ' so we will need to change either the m/hr or the time units so that they match
- 19 m/hr = -19 m/hr x 5280 f/m x 1 hr/3600 sec =19*5280/3600 = - 27.8667 ft/sec
- 27.8667 ft/sec / 10 s = - 2.78667 ft/s^2 (negative acceleration because the cyclist is slowing down)
A NEGATIVE ACCELERATION is a POSITIVE DECCELERATION
Decceleration = 2.78667 ft/s^2