Question

A boy rides a bicycle at a constant velocity. Which of the following about the net force is true? A. There is a net force acting in the velocity direction B. There is a net force acting opposite to the velocity direction C. The net force is zero D. There is a net force acting perpendicularly to the velocity direction E. None from the above The Daily Post First with the News A passenger standing in a moving bus, facing forward suddenly falls forward. This can be an indication which of the following? A. The bus speeds up B. The bus slows down C. The bus doesn't change its velocity D. The bus turns to the right E. The bus turns to the left

Answer 1

According to Newton's first law of motion, if there is no unbalanced force an object which is in rest will be in rest and a moving object will be moving at the same speed in the same direction. This means if the forces acting on the object is balanced, the state of object remains unchanged, means the acceleration of the object is zero. Newton's first law of motion sometimes referred to as the law of inertia.

If the forces are in balance (acceleration is zero), there are two possibilities:

Case-1. Acceleration and speed of the object both equal to zero.

In this case, the object will be in rest.

Case-2. Acceleration is equal to zero but speed is not equal to zero.

In this case, the object will stay in motion at the same speed and in the same direction.

(1) In the first question, the boy rides a bicycle at a constant velocity. Thus the acceleration of the boy will be equal to zero but velocity will not zero. Thus, according to the rule of inertia, the boy will be moving in the same velocity in the same direction. Thus, the force is balanced and the net force is zero.

If there is a net force acting in the direction of velocity, then the velocity of the boy will be increased.

If there is a net force acting in the opposite direction of velocity, then the velocity of the boy will be reduced.

If there is a net force acting in the perpendicular direction of velocity, then the force will not balance in the perpendicular direction, so the bicycle will fall.

Therefore, the correct option is (C).

(2) In the second question, the bus is moving, the passenger standing on the bus also moving with respect to the earth. Thus according to the rule of inertia, the passenger will the tendency to move at the same speed and in the same direction. If the bus speeds up, the passenger will fall backward, because the bus is accelerating forward and the passenger has a tendency to move at the previous speed of the bus.

And if the bus will slow down, the passenger will fall forward.

If the bus doesn't change its velocity, the passenger will be in the same position with respect to the bus.

If the bus turns to right the passenger will fall towards the left.

If the bus turns to left the passenger will fall towards the right.

Therefore, the correct option is (B).