## Force And Laws Of Motion Master Your Test Question And Answers

**Question 1. What are the effects of force?**

**Answer:** A stationary object will start moving once force is applied. Force can stop a moving object and can change the speed of the moving object. It can also change the direction of the moving object. It can also change the shape and size of an object.

**Question 2. Define contact forces.**

**Answer:** Contact force represents the result of physical contact between two objects. Ex-Normal force, frictional force etc.

**Question 3. What are field forces?**

**Answer:** If an object attracts or repels another object from a distance without being in contact is called field forces. Example: Gravitational force, electrostatic force etc.

**Question 4. Differentiate balanced and unbalanced force.**

**Answer:** A balanced force is the one in which after applying force on an object from different sides, it is still at rest. Unbalanced force is that force which produces motion in the object. In this case, the object will move in the direction of greater force.

**Question 5. Calculate the net force applied on the rope in a tug of war where rope does not move in any direction.**

**Answer:** If the rope does not move in any direction, it means balanced force is applied on it i.e., equal and opposite forces are applied from both the direction.

Therefore, the net force in this scenario will be zero.

**Question 7. Define inertia. How is inertia related to mass?**

**Answer:** Inertia is the property of inability of an object to change its state of rest or motion. Inertia of an object is directly proportional to the mass of the object.

**Question 8. What are the different kinds of inertia?**

**Answer:** There are three different kinds of inertia:

- Inertia of rest.
- Inertia of motion.
- Inertia of direction.

**Question 9. The mud from the tyres of the automobiles flies off tangentially. Why?**

**Answer:** The mud from the tyres of the automobiles flies off tangentially due to inertia of direction. Because of the absence of external force on it, the mud, when leave the rotating tyre, follow a tangential linear motion. This is the reason why mudguards are placed in the vehicles.

**Question 10. Give Reason: An athlete runs for some distance before taking a long jump.**

**Answer:** This is because of inertia of motion. When the athlete jumps and leaves the ground, his body inclines to move with the same velocity which he had before leaving the ground. And therefore, the length of the jump will hinge on the velocity of the athlete at the time when he jumps.

**Question 11. Define linear momentum. Write its SI unit.**

**Answer:** Linear momentum of an object is equal to the product of mass and velocity. The SI unit of linear momentum is kgm/s.

**Question 12. What is relation between force, mass and acceleration?**

**Answer:** Force applied on a body is equal to the product of mass and acceleration produced in the body.

**Question 13. What is the SI unit of force?**

**Answer:** SI unit of force is Newton (N) or kgm/s^{2}.

**Question 14. What is relation between two units Newton and Dyne?**

**Answer:** 1 Newton = 10^{5} Dyne

**Question 15. Calculate the force needed to speed up a car with a rate of 5 ms ^{-2}, if the mass of the car is 1000 kg.**

**Answer:**Acceleration (a) = 5 m/s

^{2}and

Mass (m) = 1000 kg,

Therefore, Force (F) =?

We know that,

F = m × a

= 1000 kg × 5 m/s^{2}

= 5000 kg m/s^{2}

Therefore, required Force = 5000 kg m/s^{2 }or 5000 N

**Question 16. An object requires the force of 100 N to achieve the acceleration ‘a’. If the mass of the object is 500 kg what will be the value of ‘a’?**

**Answer:** According to the question,

Mass (m) = 500 kg,

Force (F) = 100 N,

Acceleration (a) =?

We know that,

Force=Mass×Acceleration

or F = m × a

Therefore,

100 N = 500 kg × a

a =100N/500kg

a =100kgms^{-2}/500kg

a = 0.2 ms^{-2+}

Thus acceleration of the vehicle = 0.2 ms^{-2}

**Question 17. Define force with respect to momentum.**

**Answer:** Force is defined as the rate of change of momentum produced in an object.

**Question 18. Define conservation of momentum.**

**Answer:** Momentum of a system is constant if there are no external force acting on the system.

**Question 19. A body of mass 15 kg moving with a velocity of 15 m/s is brought to rest in 10 seconds. Find the change in momentum and also the retarding force.**

**Answer:** Mass of the body (m) = 15 kg

Initial Velocity (u) = 15 m/s

Final Velocity (v) = 0

Time (t) = 10 s

Change in momentum = mv – mu

= 15 × 0 – 15 × 15 = 0 – 225

= –225 kg m/s

Force applied is equal to rate of change in momentum.

F = mv – mu/t

= –225/10

= –22.5 N

Retarding Force = 22.5 N

**Question 20. The speed of a car weighing 1000 kg increases from 36 km/h to 108 km/h. Calculate the change in momentum.**

**Answer:** Mass of the Car (m) = 1000 kg

Initial Velocity (u) = 36 km/h (1 km/h = 5/18m/s)

= 36 × 5/18 m/s

= 10 m/s

Final Velocity (v) = 108 km/h

= 108 × 5/18 m/s

= 6 × 5

= 30 m/s

Change in momentum = mv – mu

= m(v – u)

= 1000 (30 – 10)

= 1000 × 20

Change in momentum = 20,000 N s