1.Which of the following has more inertia:
(a) a rubber ball and a stone of the same size?
(b) a bicycle and a train?
(c) a five-rupee coin and a one-rupee coin?
Ans:
Inertia depends on the mass of an object. The object with greater mass has greater inertia.
(a) Stone (because it has more mass than a rubber ball of the same size).
(b) Train (because it has much more mass than a bicycle).
(c) Five-rupee coin (because it has more mass than a one-rupee coin).
2.In the following example, try to identify the number of times the velocity of the ball changes:
“A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team.” Also, identify the agent supplying the force in each case.
Ans:
The velocity of the football changes four times:
When the first player kicks the football to another player.
When the second player kicks the football towards the goal.
When the goalkeeper stops the football.
When the goalkeeper kicks the football towards his team player.
Agents supplying the force:
a) First case: The first player.
b) Second case: The second player.
c) Third case: The goalkeeper (when stopping the football).
d) Fourth case: The goalkeeper (when kicking the football).
3.Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.
Ans: When the branch of the tree is shaken, it moves in a to-and-fro motion. The leaves, due to their inertia, resist the motion of the branch. The inertia of the leaves tries to keep them stationary while the branch moves. Leaves that are weakly attached to the branch do not have enough force to resist this motion and are detached due to inertia. On the other hand, the leaves that are firmly attached to the branch can resist this motion and remain attached.
4. Why do you fall in the forward direction when a moving bus brakes to a stop and fall backward when it accelerates from rest?
Ans: When the bus accelerates from rest, it starts moving in a forward direction. Due to inertia, the passengers resist the change in motion and experience a backward force. This is why they tend to fall backward when the bus accelerates.
When the bus is already moving and then brakes to a stop, the bus decelerates, but the passengers’ inertia causes them to continue moving forward. The passengers’ bodies want to maintain their forward motion, so they fall forward when the bus stops.
5. If action is always equal to the reaction, explain how a horse can pull a cart.
Ans: According to Newton’s third law of motion, for every action, there is an equal and opposite reaction. When the horse pulls the cart, it exerts a force on the cart in the forward direction. Simultaneously, the cart exerts an equal and opposite force on the horse, pulling it backward. However, the key point is that the horse also exerts a force on the ground with its hooves, pushing backward. The ground responds with an equal and opposite force (forward) on the horse. This forward force from the ground allows the horse to move, and since the cart is attached to the horse, the cart moves forward as well.
6. Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity?
Ans: When a fireman holds a hose ejecting large amounts of water at high velocity, the water exerts a force in the backward direction (opposite to its ejection direction). According to Newton’s third law of motion, for every action, there is an equal and opposite reaction. This reaction force from the water pushes the fireman backward. The force exerted by the water can cause the fireman to lose stability, making it difficult for him to maintain a steady position while holding the hose. Therefore, the fireman has to exert a force to counteract this backward push and stay in control.