need important question for my offline exam
Answers
Answer:
1. Suppose a ball of mass m is thrown vertically upwards with an initial speed v, its speed decreases continuously till it becomes zero. Therefore, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of the initial and final momenta of the ball are the same. Yet, it is not an example of conservation of momentum. Explain why.
Answer:
The Law of conservation of momentum is applicable to the isolated system (no external force is applied). In this case, the change in velocity is due to the gravitational force of the 0earth.
2. Why does a boat tend to leave the shore, when passengers are alighting from it?
Answer:
When the passengers alight from the boat, they push the boat in the backward direction. As a result, the boat has a tendency to slip back into the water. This difficulty is usually overcome by the boatman by tying the boat to some rigid support.
3. Why does a boat tend to leave the shore, when passengers are alighting from it?
Answer:
When the passengers alight from the boat, they push the boat in the backward direction. As a result, the boat has a tendency to slip back into the water. This difficulty is usually overcome by the boatman by tying the boat to some rigid support.
4. Describe our walking in terms of Newton’s third law of motion.
Answer:
When we walk on the ground or road, our foot pushes the ground backwards (action) and the ground pushes our foot forward (reaction). Thus, the forward reaction exerted by the ground on our feet makes us walk forward.
5. Why does a cricket player move his hand backwards while catching the ball?
Answer:
A fast-moving cricket ball has a large momentum. In stopping or catching this ball, its momentum has reduced to be zero. Now, when a cricket player moves back his hands-on catching the fastball, then the time taken to reduce the momentum of the ball to zero is increased. Due to more time taken to stop the ball, the rate of change of momentum of theball is decreased and hence a small force is exerted on the hands of the player. So, the hands of the player do not get hurt.
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