In which situation is the speed of the car constant while it's velocity is changing?

a) the car travels down a straight track at 30 m/s

b) the car travels around a circular track at 30 m/s

c) the car begins from rest and accelerates to 20 m/s

d) the car begins traveling at 30 m/s and slows to 15 m/s

i need a reply quickly ; -;

B) The car travels around a circular track at 30 m/s

Step-by-step explanation:

The key to correct answer is difference between speed and velocity.

Speed is distance covered in particular time while velocity is distance covered by body in particular time in defined direction.

Now, for option A, neither speed nor direction is changing. So this option is excluded.

For option C and D, there is positive and negative acceleration exists, even if direction is constant, so magnitude of speed is changing here, so these two options are also excluded.

Now, for option B, one can see that due to circular motion, the speed is constant at 30m/s but direction is changing continuously due to circular motion. So, speed is constant but velocity is changing. Hence, B is the right answer.

depends what are you allowed to do ?