Chapter 1: About Science
Exercise 2: B is the hypothesis.
Exercise 3: His hypothesis was partially correct. If a plant is grown in a known mass of soil the after a considerable amount of time, when amount mass of plant gained is compared with amount of mass lost by soil. They are not the same.
Exercise 5: Example :Hydroelectricity. Advantages: clean power, irrigation. Disadvantage : floods, etc.
Exercise 7: The person is thinking theory to be a guess or a myth.
Exercise 9: Length of shadow of pole would be different and thus overall ratio of 1:8 would be diferent.
Chapter 2: Newton’s 1st Law of Motion.
Exercise 10: Pulling the cloth upward would tend to lift the dishes. The trick is to pull the cloth without disturbing the dishes, thus demonstrating 1st law of motion.
Exercise 20: Maximum result will be obtained by applying both in the same direction: 32 N
Minimum result will be obtained by applying both opposite to each other: 8 N
Exercise 30: 800N. Pulley will only change the direction of applied force.
Exercise 40: Support force provided by floor decrease and support force on workmen’s increases as they start to lift the crate.
Exercise 48: This is because plane’s speed is measured relative to air. In absence of air speed will be equal.
Chapter 3: Linear Motion.
Exercise 5: Light travels at a constant speed. It doesn’t have any acceleration.
Exercise 15: Highest point in the path of a ball thrown upward.
Exercise 25: Speed will increase by 9.8m/s with every second.
Exercise 35: Acceleration due to gravity will be same in all the instances. Speed may differ along the trajectory but since gravity is the only acting, once the projectile is launched so acceleration is same.
Exercise 45: Question1 Consider a cylinder rolling on a table top. Since no further force is applied once it started moving which statement is true
1. Velocity is constant
2. Acceleration is constant
3. None of the above.
Question 2 A plane flying along curved path at constant speed changes what ?
1. Acceleration.
2. Velocity
3. None of the above.
Chapter 4 Newton’s 2nd Law of Motion.
Exercise 10: Since you are carrying a heavier load it takes longer to come to a complete stop after hitting the wall, since it has greater inertia than an empty hand.
Exercise 20: 2nd law F=ma
If force is zero the acceleration is zero.
Exercise 30: Same amount of force acts on the coin through out.
Exercise 40: It contains energy which generates force.
Exercise 50: In first case book pushes on paper and both fall together. In second case, as the book falls moving air out of its way, creating a high pressure zone under the book and low pressure on top. As air moves towards low pressure zones it keeps the paper with the book. Since there is no air drag on paper they both fall together.
Chapter 5: Newton’s 3rd Law of Motion.
Exercise 10: Foot exerts force on the ball and the ball exerts force on the foot. Both forces are equal and opposite.
Exercise 20: As the horse tries to pull the wagon it will try to pull
