Q1. The time period of a pendulum depends on
(a) the mass
(b) the length
(c) the time
(d) both (a) and (b)
Q2. Which of the following is the smallest unit of length?
Q3. A man is standing on a boat in still water. If he walks towards the shore, the boat will
(a) move towards the shore
(b) move away from the shore
(c) remain stationary
Q5. A body travelling with a speed of more than the velocity of sound in air is said to travel with
(a) supersonic speed
(b) hypersonic speed
(c) ultrasonic speed
(d) infrasonic speed
Q6. A passenger in a moving train tosses a coin. If the coin falls behind him, the train must be moving with
(a) an acceleration
(b) a deceleration
(c) a uniform speed
(d) none of the above
Q7. China wares are wrapped in straw of paper before packing. This is the application of concept of
(d) none of the above
Q8. When a body is stationary, then
(a) there is no force acting on it
(b) the body is in vacuum
(c) the force acting on it is not in contact with it
(d) the net forces acting on it balances each other
Q9. What happens when a heavy object and a light object are allowed to fall from the certain height in the absence of air
(a) heavy object reaches the ground later than the lighter object
(b) lighter object reaches the ground later than the heavier object
(c) both heavy and light objects reach the ground simultaneously
(d) None of these
Q10. An artificial satellite orbiting the earth does not fall down because the earth’s attraction
(a) is balanced by the attraction of the moon
(b) vanishes at such distances
(c) is balanced by the viscous drag produced by the atmosphere
(d) produces the necessary acceleration of its motion in a curved path
S1. Ans (b)
Sol. Time period T = 2π√(l/g) . The time period of a pendulum depends on its length l and acceleration due to gravity g.
S3. Ans (b)
Sol. According to Newton’s third law of motion, every action has an equal and opposite reaction. This implies that force always occurs in pairs where if object a exerts a force “F” on object B, then object B exerts an equal and opposite force “—F” on object A. Thus, if a man standing on a boat in still water begins to walk towards the shore then in response to this , the boat will start moving away from the shore.
S4. Ans (a)
S5. Ans (a)
Sol. Supersonic speed is a rate of travel of an object that exceeds the speed of sound. For objects travelling in dry air of a temperature of 20°C at sea level, this speed is approximately 343 m/s.
S6. Ans (a)
Sol. If the train were moving with uniform velocity, the coin would fall back to the passenger’s hand. While, if the train is accelerated, the horizontal velocity of the train would be more than that of the coin by the time the coin returns. Therefore, the train travels a greater horizontal distance than the coin and coin falls behind the passenger.
S7. Ans (a)
Sol. As a certain impulse applied for a short time will give a large force so the chinaware breaks into pieces. Therefore, chinaware is wrapped in straw of paper while packing so that the event of fall (impact) will take a longer time to reach the chinaware through straw of paper and hence the average force exerted on the chinaware is small and chances of its breaking reduce.
S8. Ans (d) For both stationary and moving objects with unchanging speed and direction, all the forces acting on the objects are in balance with each other, i.e. they all cancel each other.
S9. Ans (c)
Sol. If no air resistance is present, the rate of descent depends only on how far the object has fallen, no matter how heavy the object is. This means that two objects will reach the ground at the same time if they are dropped simultaneously from the same height.
This statement follows from the law of conservation of energy. However, if air resistance is present, then the shape of the object becomes important.
Sol. An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of earth provides the necessary acceleration for its motion. This acceleration is “constant” in magnitude but “changing in direction”. By the launch rocket, immediately before the satellite is established in the predetermined orbit, the speed given to it is 30,000 km/hr. The speed must be great enough so gravity brings the satellite back to Earth but not so great that the satellite escapes gravity out into space.