Question

7.How long (în seconds) does it take for a rocket sledaccelerating at 15.0 m/s2 to change its speed from20.0 m/s to 65.0 m/s?

Answer 1

The acceleration (a) of an object is the rate of change of its velocity with respect to time:

`a=(v_f-v_0)/(\Delta t)`

Since the rocket has a constant acceleration of 15.0m/s^2, its initial speed is 20.0m/s and its final speed is 65.0m/s, then, the only unkown in the equation above is the time interval Δt.

Isolate Δt from the equation and replace the value of the known variables to find the time that it takes for the rocket to reach a speed of 65m/s if it starts from 20.0m/s, with a constant acceleration of 15.0m/s^2:

`\Delta t=(v_f-v_0)/(a)=(65.0(m)/(s)-20.0(m)/(s))/(15.0(m)/(s^2))=(45.0(m)/(s))/(15.0(m)/(s^2))=3.00s`

Therefore, it takes 3.00 seconds for the rocket to change its speed from 20.0m/s to 65.0m/s.