Question

determine in the following scenarios if the net force is zero or not.

et force is zero\ = no force applied

et force not zero\ = there is a force applied
a person pushes against a large rock and the rock doesnt move.
jim put on his brakes while he was riding his bicycle.
a truck speeds up from 0 miles/hour to 40 miles/hour.
a bird was flying in the direction of north, when a wind suddenly changed its direction to
a car travels at a constant speed

Explanation:

1. A person pushes against a large rock and the rock doesn't move: When the rock doesn't move, the applied force (push) is balanced by the static friction force. So net force is zero (since there's no acceleration, \( F_{net} = ma = m \times 0 = 0 \)).
2. Jim put on his brakes while he was riding his bicycle: Braking causes a frictional force that slows the bicycle, changing its velocity (deceleration). So there's a net force (not zero) because acceleration (deceleration) exists.
3. A truck speeds up from 0 miles/hour to 40 miles/hour: Speeding up means acceleration (\( a = \frac{\Delta v}{\Delta t} > 0 \)). By Newton’s second law, \( F_{net} = ma \), so net force is not zero (since \( a

eq 0 \)).

1. A bird was flying north, wind changed its direction to northeast: A change in direction means a change in velocity (vector), so acceleration exists. Thus, net force is not zero (since \( F_{net} = ma \) and \( a

eq 0 \)).

1. A car travels at a constant speed: If speed and direction are constant, velocity is constant (\( \Delta v = 0 \)), so acceleration \( a = 0 \). Thus, \( F_{net} = ma = 0 \) (net force is zero, assuming no direction change; if direction is constant, constant speed implies zero net force).

Answer:

1. A person pushes against a large rock and the rock doesn’t move: Net Force is Zero
2. Jim put on his brakes while he was riding his bicycle: Net Force NOT Zero
3. A truck speeds up from 0 miles/hour to 40 miles/hour: Net Force NOT Zero
4. A bird was flying north, wind changed its direction to northeast: Net Force NOT Zero
5. A car travels at a constant speed: Net Force is Zero