JEE Physics Laws Of Motion MCQs Set 03

Question. In a rocket, fuel burns at the rate of 1 kg/s. This fuel is ejected from the rocket with a velocity of 60 km/s. This exerts a force on the rocket equal to
(a) 60000 N
(b) 6000 N
(c) 60 N
(d) 600 N

Answer: A

Question. A man fires a bullet of mass 200 gm at a speed of 5 m/s. The gun is of one kg mass. By what velocity the gun rebounds backward?
(a) 1 m/s
(b) 0.01 m/s
(c) 0.1 m/s
(d) 10 m/s

Answer: A

Question.  A 10 N force is applied on a body produces in it an acceleration of 1 m/s². The mass of the body is
(a) 10 kg
(b) 5 kg
(c) 20 kg
(d) 15 kg

Answer: A

Question. force of 6 N acts on a body at rest and of mass 1 kg. During this time, the body attains a velocity of 30 m/s. The time for which the force acts on the body is
(a) 5 second
(b) 7 second
(c) 10 second
(d) 8 second

Answer: A

Question. A shell, in flight, explodes into four unequal parts
(a) Momentum
(b) Kinetic energy
(c) Potential energy
(d) None of this

Answer: A

Question. A 5000 kg rocket is set for vertical firing. The exhaust speed is 800 ms^–1. To give an initial upward acceleration of 20 ms^–2, the amount of gas ejected per second to supply the needed thrust will be (g= 10 ms^–2)
(a) 187.5 kg s^–1
(b) 185.5 kg s^–1
(c) 127.5 kg s^–1
(d) 137.5 kg s^–1

Answer: A

Question. A bullet is fired from a gun. The force on the bullet is given by F = 600 – 2 x 10⁵ t, where F is in newton and t in second. The force on the bullet becomes zero as soon as it leaves the barrel. What is the impulse imparted to the bullet? 
(a) 0.9 Ns
(b) 1.8 Ns
(c) 0
(d) 9 Ns

Answer: A

Question. A ball of mass 0.25 kg attached to the end of a string of length 1.96 m is moving in a horizontal circle. The string will break if the tension is more than 25 N. What is the maximum speed with which the ball can be moved?
(a) 14 m/s
(b) 3.92 m/s
(c) 3 m/s
(d) 5 m/s

Answer: A

Question. A mass of 1 kg is suspended by a thread. It is (i) lifted up with an acceleration 4.9 m/s², (ii) lowered with an acceleration 4.9 m/s². The ratio of the tensions is
(a) 3 : 1
(b) 2 : 1
(c) 1 : 2
(d) 1 : 3

Answer: A

Question. If the force on a rocket, that releases the exhaust gases with a velocity of 300 m/s is 210 N, then the rate of combustion of the fuel is
(a) 0.7 kg/s
(b) 10.7 kg/s
(c) 1.4 kg/s
(d) 0.07 kg/s

Answer: A

Question. A 500 kg car takes a round turn of radius 50 m with a velocity of 36 km/h. The centripetal force is
(a) 1000 N
(b) 750 N
(c) 1200 N
(d) 250 N

Answer: A

Question. An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of 12 ms^–1 and the second part of mass 2 kg moves with 8 ms^–1 speed. If the third part flies off with 4 ms^–1 speed, then its mass is
(a) 5 kg
(b) 7 kg
(c) 17 kg
(d) 3 kg

Answer: A

Question. A cricketer catches a ball of mass 150 g in 0.1 s moving with speed 20 m/s, then he experiences force of
(a) 30 N
(b) 300 N
(c) 3 N
(d) 0.3 N

Answer: A

Question. A lift of mass 1000 kg is moving with acceleration of 1 m/s² in upward direction, then the tension developed in string which is connected to lift is
(a) 10,800 N
(b) 11,000 N
(c) 10,000 N
(d) 9800 N

Answer: A

Question. A monkey of mass 20 kg is holding a vertical rope. The rope will not break when a mass of 25 kg is suspended from it but will break if the mass exceeds 25 kg. What is the maximum acceleration with which the monkey can climb up along the rope? (g = 10 m/s²)
(a) 2.5 m/s²
(b) 25 m/s²
(c) 10 m/s²
(d) 5 m/s²

Answer: A

Question. A man weighs 80 kg. He stands on a weighing scale in a lift which is moving upwards with a uniform acceleration of 5 m/s². What would be the reading on the scale? (g = 10 m/s²)
(a) 1200 N
(b) 800 N
(c) 400 N
(d) Zero

Answer: A

Question. A roller coaster is designed such that riders experience “weightlessness” as they go round the top of a hill whose radius of curvature is 20 m. The speed of the car at the top of the hill is between
(a) 14 m/s and 15 m/s
(b) 13 m/s and 14 m/s
(c) 15 m/s and 16 m/s
(d) 16 m/s and 17 m/s

Answer: A

Question. The mass of a lift is 2000 kg. When the tension in the supporting cable is 28000 N, then its acceleration is
(a) 4 ms^–2 upwards
(b) 4 ms^–2 downwards
(c) 30 ms^–2 downwards
(d) 14 ms^–2 upwards

Answer: A

Question. An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are, 1 kg first part moving with a velocity of 12 ms^–1 and 2 kg second part moving with a velocity of 8 ms^–1. If the third part flies off with a velocity of 4 ms^–1, its mass would be
(a) 5 kg
(b) 3 kg
(c) 7 kg
(d) 17 kg

Answer: A

Question. A man of 50 kg mass is standing in a gravity free space at a height of 10 m above the floor. He throws a stone of 0.5 kg mass downwards with a speed 2 m/s. When the stone reaches the floor, the distance of the man above the floor will be
(a) 10.1 m
(b) 10 m
(c) 9.9 m
(d) 20 m

Answer: A