Force and Pressure Test - 4

When a force is applied at an object moving or at rest, the object experiences a change in its state. The speed of the object will increase if the force is applied in the direction of the motion.

Hence option A is the correct answer.

Contact forces are such forces that can only be applied on the body if they are in contact. For example, muscular forces can only be applied when the agent is in contact with the object. Similarly, in the elastic spring force the there is a contact between the spring and the agent. Hence, it is an example of non-contact force.

In electrostatic force, the force can be applied even if there is no contact between the two bodies. Therefore, it is an example of non-contact force. So, option B is the correct answer.

The force exerted by a liquid increases with increase in the depth. As the depth increases, the pressure exerted on the wall also increases. Hence, option A is the correct answer.

The weight of a body is balanced by the up-thrust of water. A body only floats in case the weight of the body is equal to the buoyant force exerted by the liquid on the body. Hence, the net force acting on a body is zero and so this helps the body float.

Thus option B is the correct answer.

The weight of an object is equal to the product of its mass and the acceleration due to gravity. 

W = Mg

Since, weight is the result of gravitational force acting on an object, there is no gravitational force acting on the astronaut and so, the weight of an astronaut in outer space will be zero.

A contact force can be described as the force that is caused by the action that involves contact; for example, a farmer ploughing his field to sow seeds. The action of plough going through the soil surface involves a contact. Thus it is an example of contact force.

In the question above, the action of magnet picking up safety pins involves no contact of the pin for the magnets to pick up the pins. The pins are attracted towards the magnet due to the magnetic force that requires no contact.

A balloon inclining towards a rubbed stick is an example of electrostatic force. Electrostatic forces are attractive or repulsive forces between particles that are caused by their electric charges. It requires no contact for the forces to act.

Moon orbiting earth is a classic example of gravitational force that exist between two matter in the universe.

Although the opposing force exerted by a track on the wheels is an example of contact force as the wheel is in contact with the track for the frictional force to occur on the wheels

The magnitude of the non-contact force depends on the distance between two bodies, mass and chemical composition of the two bodies.
The strength of the gravitational force depends on the mass of the matters in consideration. And it weakens if the distance between the matters is increased. Thus it depends on both the masses and the distance between them. 
Most of the non-contact forces also bring changes in the chemical composition of the substance. 

Thus option D is the correct answer.

Raghav uses his arms to rotate the lever which draws the bucket out of the well. Hence, he uses his muscular power to pull the bucket. The correct answer is C.

A magnet attracts a magnetic material thereby making it move from rest. There may be a temporary change in the shape or size. But there is no change in the chemical composition.

Hence option D is the correct answer.