Which of these is an example of acceleration?

a bicyclist turning around a corner
a car traveling south with its cruise control set
a bus traveling north at 25m/s
a helicopter waiting to take off

The bicyclist turning around a corner

Explanation:

Acceleration is caused by either change in magnitude or direction of the velocity of a body. Acceleration is given by rate of change of velocity over time. Hence, for acceleration to have a non-zero value, the velocity of the object must change.

In case 2, the car is in cruise control, which is basically a constant velocity motion and also the direction of motion is fixed i.e. south, hence no acceleration.

In case 3, the bus is travelling at a constant speed towards north i.e. fixed speed and fixed direction. Again, no acceleration.

In case 4, the helicopter is waiting to take off, i.e. it is at rest, with velocity 0. Hence, no acceleration.

However, in case 1, the bicyclist is turning around a corner which is circular motion. Although the velocity magnitude might be constant, its direction is continuously changing along the corner. Hence, the bicycle is accelerating.

The bicyclist turning around a corner

Explanation:...

explanation:

as the height from which the ruler was dropped increased, the speed of the ruler at ryan's hand increased.

the answer is b, have negligible mass