Question

hw #2 kinematic equations
equations to use
v = δx/δt
x_f=x_i + vt
x_f=x_i+v_it + 1/2at^2
a = δv/δt
v_f=v_i+at
v_f^2=v_i^2+2aδx
a_g = 9.8m/s^2

1. what is the difference between speed and velocity?
2. when would the velocity and acceleration of an object be in the same direction?
3. when would the velocity and acceleration of an object be in opposite directions?
4. if a ball is thrown straight into the air, what would the velocity be at the top of the trajectory?
5. your car has a device that tells you how fast you are traveling. why is this device called a speedometer instead of a velocitymeter?

Explanation:

1. Speed is a scalar quantity representing how fast an object moves, while velocity is a vector quantity that includes both speed and direction of motion.
2. The velocity and acceleration of an object are in the same direction when the object is speeding up. For example, a car accelerating forward has forward - directed velocity and acceleration.
3. The velocity and acceleration of an object are in opposite directions when the object is slowing down. For instance, a car applying brakes while moving forward has forward - directed velocity but backward - directed acceleration.
4. When a ball is thrown straight up into the air, at the top of its trajectory, its velocity is 0 m/s. At this instant, the ball stops moving upward before starting to fall back down.
5. A speedometer in a car measures speed because it only gives information about how fast the car is moving (a scalar value) and does not provide any information about the direction of motion.

Answer:

1. Speed is scalar, velocity is vector (speed + direction).
2. When the object is speeding up.
3. When the object is slowing down.
4. 0 m/s.
5. Because it only measures speed (a scalar), not direction.