The car's initial velocity is 0 km/hr since it starts from rest. We need to convert the velocity to m/s to calculate the acceleration.

9.0 km/hr = 2.5 m/s

Using the formula for acceleration:

a = (v - u) / t

where a is acceleration, v is final velocity, u is initial velocity, and t is time

a = (2.5 m/s - 0 m/s) / 3 hours

a = 0.83 m/s²

Therefore, the acceleration of the car is 0.83 m/s².

The bike's initial velocity is 20 m/s. We can use the same formula for acceleration:

a = (v - u) / t

where a is acceleration, v is final velocity, u is initial velocity, and t is time

a = (0 m/s - 20 m/s) / 2.0 s

a = -10 m/s² (note the negative sign indicates deceleration)

Therefore, the acceleration of the bike is -10 m/s².

The car's initial velocity is 10 m/s, acceleration is 50 m/s², and time is 3 seconds. We can use the formula for final velocity:

v = u + at

where v is final velocity, u is initial velocity, a is acceleration, and t is time

v = 10 m/s + (50 m/s²)(3 s)

v = 160 m/s

Therefore, the final velocity of the car is 160 m/s.

We can use the formula for acceleration to calculate the time it takes to change speed from 8 m/s to 12 m/s, assuming constant acceleration:

a = (v - u) / t

where a is acceleration, v is final velocity, u is initial velocity, and t is time

a = (12 m/s - 8 m/s) / t

a = 4 m/s²

Substituting the acceleration and initial velocity values into the formula:

t = (v - u) / a

t = (12 m/s - 8 m/s) / 4 m/s²

t = 1 s

Therefore, it will take 1 second for the object to change its speed from 8 m/s to 12 m/s.