Class 9 Force and Laws of Motion Important Questions

Important Questions Notes NCERT Solutions MCQ Quiz – 1 MCQ Quiz – 2

Force and Laws of Motion Important Questions

1. Using second law of motion, derive the relation between force & acceleration. A bullet of 10 g strikes a sand-bag at a speed of 1000 m/s & gets embedded after travelling 5 cm. Calculate :
   1. the resistive force exerted by the sand on the bullet
   2. the time taken by the bullet to come to rest.
2. A truck of mass M is moved under a force F. If the truck is then loaded with an object equal to the mass of the truck & the driving force is halved, then how does the acceleration change?
3. A stone of 1 kg is thrown with a velocity of 20 m/s across the frozen surface of a lake & comes to rest after travelling a distance of 50 m. What is the force of friction between the stone & the ice?
4. Two objects of masses 100 g & 200 g are moving along the same line & direction with velocities 2 m/s & 1 m/s respectively. They collide & after the collision, the first object moves at a velocity of 1.67 m/s. Determine the velocity of the second object.
5. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m/s before the collision during which they stick together. What will be the velocity of the combined object after collision?
6. A bus of mass 5000 kg starts from rest & rolls down a hill. If it travels a distance of 200 m in 10 s, calculate (i) acceleration of the bus & (ii) the force acting on the bus.
7. A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration & change in momentum. Also, calculate the magnitude of the force required.
8. An automobile vehicle has a mass of 1600 kg. What must be the force between the vehicle & road if the vehicle is to be stopped with to be a negative acceleration of 1.7 m/s² ?
9. A hockey ball of mass 250 g travelling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 5 m/s. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
10. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m/s before the collision during which the stick together. What will be the velocity of the combined object after collision?
11. An object of mass 100 kg is accelerated uniformly from a velocity of 5 m/s to 8 m/s in 6 s. Calculate the initial & final momentum of the object. Also, find the magnitude of the force exerted on the object.
12. Why does a person pull his hands backwards while catching a ball?
13. One hockey player has a mass of 50 kg was moving with a velocity of 5 m/s & the other player of mass 60 kg moves towards him with velocity of 6 m/s . While playing they collide & get entangled. With what velocity & in which direction will they move after collision. Ignore friction.