Example Solutions
1. Does a car speedometer measure speed, velocity, or both?
Speed is a scalar quantity that tells us how fast an object is traveling only. It does not tell us the direction the object is moving.
Velocity is a vector quantity that tells us the direction an object is going and how fast it's traveling.
Since a car speedometer only tells us how fast
the car is going and not the direction it only measures speed.
2.
Can an object have a northward velocity and a southward acceleration?
Explain.
Yes. When a car heading north is braking, it has a northward velocity but it
is slowing down, so it has an acceleration in the opposite direction, i.e. a
southward acceleration.
3. Give an example where both the velocity and acceleration are negative.
Assume the
You can throw a stone straight up, when it eventually comes down its velocity points downward, thus is negarive, and its acceleration, 9.8 m/s squared are negative.
4. As a
freely falling object speeds up, what is happening to its acceleration due
to gravity — does it increase, decrease, or stay the same?
For any free-falling object, its acceleration stays constant at 9.8 m/s2.
It does not matter whether the object is going up or down, whether the
object is speeding up or slowing down.
5. Can an object have zero velocity and nonzero acceleration at the same time? Give examples.
An object can have zero velocity and nonzero acceleration
at the same time.
Consider a ball thrown upwards. At the maximum height, velocity becomes zero for an instant. But, it will experience acceleration downwards due to gravity. If the acceleration were zero, the velocity would remain zero at the highest point, and the ball would stay up there without falling.
Same is in the case of a simple pendulum. At the point of
maximum displacement, the velocity will become momentarily zero. But, the
acceleration will have a positive value equal to the acceleration due to
gravity.