A rock thrown straight up reaches its highest point at 1.5 s. What are its velocity and acceleration at that instant?
AVelocity -9.80 m/s and acceleration zero
BVelocity zero and acceleration zero as well
CVelocity zero and acceleration -9.80 m/s^2
DVelocity 13.0 m/s and acceleration -9.80 m/s^2
Answer & Solution
Correct answer: C. Velocity zero and acceleration -9.80 m/s^2
1. On the way up the rock slows because gravity opposes its motion.
2. At the highest point the upward velocity has fallen to zero.
3. Gravity does not switch off there, so the acceleration is still -9.80 m/s^2.
4. That acceleration holds for the whole trip, going up and coming down alike.
5. Assuming zero velocity implies zero acceleration is the classic trap here.
6. A velocity of -9.80 m/s confuses the value of the acceleration with a velocity.
_Source: OpenStax College Physics (CC BY 4.0), Ch 2 "Kinematics", section 2.7 Falling Objects_
Related questions
Measuring time at all depends on the fact that:An airplane passenger moving 4 metres toward the rear of the plane has a displacement recoA cyclist rides 3 km west then turns and rides 2 km east. The magnitude of the displacemenA scalar such as temperature can be negative, and there the minus sign indicates:An object with negative acceleration whose acceleration points the same way as its motion Deceleration is best defined as acceleration that is:An acceleration of 8.33 metres per second squared due west means the velocity changes by:The SI unit of acceleration is metres per second per second because acceleration is: