Question

day 5 - 8th grade science staar reviewname kimberly mirandadate 2/12/26force, motion, and energy - teks 8.6c (r), 7.7a (s), 6.8a (s), 6.9c (s)1. samuel kicks a soccer ball across a grassy field and it eventually comes to a stop. if newtons law of inertia is true, why did the ball stop?a newtons law only applies to objects at rest.b the mass of the ball is not great enough to have inertia.c friction with the grass applies a net force on the ball causing it to decrease its speed.d gravity slowed the ball until it came to a stop.2. once in orbit, the space shuttle used very little, if any, rocket power to maintain its speed despite traveling over 15,000 mph! how were nasa engineers able to do this?a the space shuttle is very massive and must burn its rockets at full power to achieve this speed.b the space shuttle was able to use a special coating in order to achieve its fast speed in space.c gravity provides the necessary force to keep the space shuttle traveling at a high rate of speed.d the speed generated from force of rockets during liftoff is maintained throughout the flight since there is no air friction.3. in the case of a car crash, the bodys inertia will continue to carry it in its initial direction. however, if the person is wearing a seatbelt, in which direction will this force act?a to the rightb to the leftc upwardd downward4. suppose you pull nick, who is standing on a skateboard, using a rope at a constant acceleration. nicks friend, who weighs the same as nick, then gets on the skateboard too. how is the force you have to apply to the rope affected to maintain the same constant acceleration?a there will be no change to the required amount of force.b the amount of force required is slightly increased.c the amount of force required is doubled.d the amount of force required is four-times as great.

Explanation:

1. For question 1: Newton's first law (inertia) states objects maintain motion unless acted on by an unbalanced force. Friction from grass opposes the ball's motion, slowing it to a stop.
2. For question 2: In orbit, once the shuttle reaches the required speed, it moves in a path where gravity provides the centripetal force needed to maintain its orbital speed without constant rocket thrust.
3. For question 3: When a car crashes and stops suddenly, the person's inertia keeps them moving forward. A seatbelt applies a force opposite to this motion (to the left, assuming the car was moving right as implied by the crash direction) to stop the person.
4. For question 4: Using Newton's second law $F=ma$, if acceleration is constant and mass doubles (adding a friend of equal mass), the required force must double to maintain the same acceleration.

Answer:

1. C. Friction with the grass applies a net force on the ball causing it to decrease its speed.
2. C. Gravity provides the necessary force to keep the space shuttle traveling at a high rate of speed.
3. B. to the left
4. C. The amount of force required is doubled.