Question

1. which is an example of negative work? why?

a. kicking a ball kicking a ball makes it move faster and go forward
b. catching a ball catching a ball will make your hands push agains
c. spinning a ball makes the ball rotate not slow down so wrong
d. carrying a ball not moving the ball up or down so false

Explanation:

To determine negative work, recall that work \( W = F \cdot d \cdot \cos\theta \), where \( \theta \) is the angle between force and displacement. Negative work occurs when \( \cos\theta<0 \) (force and displacement are opposite).

• Option a: Kicking a ball applies force in the direction of motion (\( \theta = 0^\circ \), \( \cos\theta = 1 \)), so work is positive.
• Option b: When catching a ball, your hands apply a force opposite to the ball’s displacement (to stop it). Here, \( \theta = 180^\circ \), \( \cos\theta=-1 \), so work is negative.
• Option c: Spinning a ball involves torque (rotational force), not linear work in the context of negative work here. The explanation also indicates it is incorrect.
• Option d: Carrying a ball horizontally (if height doesn’t change) has force (gravity) vertical and displacement horizontal (\( \theta = 90^\circ \), \( \cos\theta = 0 \)), so work is zero, not negative.

Answer:

b. catching a ball Catching a ball will make your hands push against the ball's motion (force opposite to displacement), resulting in negative work.