This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Newton’s Second Law of Motion”.
1. What is the force applied on a body with 5 kg of mass and an acceleration of 7 m/s2?
a) 35 N
b) 5 N
c) 7 N
d) 0 N
Explanation: According to the second law of motion, the force on a body is equal to the rate change of its momentum. On simplifying we get, F = ma. Therefore, Force = 5 x 7 = 35 N.
2. Unit of force is _____
Explanation: The unit of force is newton. This unit has been given after the name of the famous scientist Sir Isaac Newton who had given the three laws of motion. The force on anybody can be found with the help of the second law of motion.
3. The unit ‘Newton’ is equivalent to ______
Explanation: From the second law of motion we get that F = ma, when the mass is not changing. Putting in the units, we get, Newton = Kg-m/s2.
4. If the force acting on a body is 10 N, and the acceleration is 4 m/s2, what can be the mass of the body?
a) 2.5 Kg
b) 25 Kg
c) 0.25 Kg
d) 5 Kg
Explanation: From the second law of motion we get that F = ma, when the mass is not changing. Putting in the values, we get, Force = 10 = m x 4. Which will result in m = 2.5 Kg.
5. If the force acting on a body is 50 N, and the mass is 5 kg, what can be the acceleration of the body?
a) 10 m/s2
b) 80 m/s2
c) 8 m/s2
d) 0.8 m/s2
Explanation: From the second law of motion we get that F = ma, when the mass is not changing. Putting in the values, we get, Force = 10 = 5 x a. Which will result in a = 10 m/s2.
6. An example of variable mass system is _____
a) A car moving
b) A rocket taking off
c) A bicycle moving
d) A man walking
Explanation: In case of a rocket taking off, the mass of the fuel is large and cannot be neglected. As the rocket starts moving, a large amount of fuel is getting burnt out from the nozzle, hence the total mass decreases. Hence it is a variable mass system.
7. How do we calculate force in a variable mass constant velocity system?
a) F = ma
b) F = mv
c) F = v(dm/dt)
d) F = m/t
Explanation: The general expression for force is F = dp/dt. On solving we get, F = m(dv/dt) + v(dm/dt). Since the system is constant velocity, hence dv/dt = 0. What remains is F = v(dm/dt).
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