Physics - Study Mode

[#861] A metal ball and a rubber ball, both having the same mass, strike a wall normally with the same velocity. The rubber ball rebounds and the metal ball does not rebound. It can be concluded that
Correct Answer

(A) The rubber ball suffers greater change in momentum

Explanation

Solution: As per the question, the rubber ball rebounds while the metal ball does not. So if m and v be the mass and velocity respectively, the change in momentum of rubber ball = 2 mv (in magnitude). However, the change in momentum of the metal ball = mv. The rubber ball suffers almost twice the change in momentum as experienced by the metal ball.

[#862] A boy sitting in an open car moving with the constant speed throws a ball straight up into the air. The ball falls
Correct Answer

(A) Behind him

Explanation

Solution: The moment ball is thrown, it is moving with the velocity of the car. According to the inertia of motion it will continue to move in the same direction with the same velocity. As the ball is moving up and the down it will maintain its forward motion but practically it is not possible to neglect the resistance caused by air friction. So, the ball will fall behind him. Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion.

[#863] Rate of change of momentum is
Correct Answer

(C) Force

Explanation

Solution: The rate of change of linear momentum of a body is directly proportional to the external force applied on the body , and takes place always in the direction of the force applied.

[#864] Which law is also called law of inertia ?
Correct Answer

(A) Newton first law

Explanation

Solution: Newton first law is called law of inertia.

[#865] A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of the emf's is :
Correct Answer

(D) 3:2

Explanation

Solution: In series : E1 + E2 = K(50) In parallel : E1 - E2 = K(10) E1 + E2 / E1 - E2 = 5/1 => E1/E2 = 3/2 The emf's are in the ratio of 3:2.