NCERT Class VIII Science Solutions: Chapter 11-Force and Pressure Part 4

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SHORT ANSWER QUESTIONS

Question 18:

A chapati maker is a machine which converts balls of dough into chapati’s. What effect of force comes into play in this process?

Answer:

The force changes the shape of the dough

Question 19:

As showing in fig is a the parachute

The Parachute

As showing in fig is a the parachute

Fig shows a man with a parachute. Name the force which is responsible for his downward motion. Will he come down with the same speed without the parachute?

Answer:

Force of gravity. No, without the parachute his speed will be higher

Question 20:

Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied.

Answer:

The magnitude of forces will be equal and it acts in opposite’s direction, so that they are cancelling each other. We can understood this by using the following diagram.

Image of show to magnitude of forces

Image of Show to Magnitude of Forces

Image of show to magnitude of forces

Question 21:

Two Thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.

Answer:

Electrostatic force. The balls have similar charges. They move away due to repulsion between similar charges

Question 22:

Fruits detached from a tree fall down due to force of gravity. We know that a force arises due to interaction between two objects. Name the objects interacting in this case.

Answer:

Earth and fruits

Question 23:

A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he wants to slow it down. What should he do?

Answer:

Man can do following things:

  1. He can start pulling the cart instead of pushing it in order to balance the downward force due to gravity.

  2. He can go the other side by moving himself very fast in the direction of motion and try to slow down the speed of cart by giving an opposite force to the moving cart.