What is the direction and sign of acceleration in each case.
A) stone was dropped from the top of a cliff. Neglect air drag.
b) tennis player hits a ball with a racket.
c) boy kicks in a soccer ball
gravity always applies downward force, so acceleration is down
depending on whether the tennis racket or foot is moving up or down, apply the appropriate force from that source.
a. if z is up, g is down, negative
acceleration = -9.81 m/s^2 around here
b. If the player is looking toward the net, the force by the racket and resulting acceleration are positive.
c. again if x is forward the force of the foot on the ball and the acceleration are positive
HOWEVER - I think this question is questionable. If you define your directions opposite, your signs change.
To determine the direction and sign of acceleration in each case, we need to understand the concept of acceleration and its calculation.
Acceleration is the rate at which an object's velocity changes over time. It can be calculated using the formula:
acceleration = (final velocity - initial velocity) / time
Now let's analyze each case:
A) Stone was dropped from the top of a cliff. Neglect air drag.
In this case, the stone is initially at rest. As it falls due to gravity, its velocity increases in the downward direction. So, the direction of acceleration is downward, or towards the center of the Earth. The sign of acceleration is usually taken as negative (-) in the downward direction.
B) Tennis player hits a ball with a racket.
When a tennis player hits a ball with a racket, the ball experiences a change in velocity due to the impact. The direction of acceleration depends on the force applied. If the tennis player hits the ball in the same direction as its initial motion (e.g., when serving), the acceleration will be in the same direction. However, if the tennis player hits the ball opposite to its initial motion (e.g., when returning a shot), the acceleration will be in the opposite direction. The sign of acceleration can be positive (+) or negative (-), depending on the direction of the hit.
C) Boy kicks a soccer ball.
When a boy kicks a soccer ball, the ball's velocity changes due to the impact of the kick. The direction of acceleration will depend on the force and direction of the kick. If the boy kicks the ball towards a specific direction, the acceleration will be in that direction. The sign of acceleration can be positive (+) or negative (-), depending on the direction of the kick.
In conclusion, the direction and sign of acceleration in each case depend on the specific circumstances and the forces involved. It is essential to analyze the forces acting on the object to determine the direction and sign of acceleration accurately.