Newton : Tut 1

1. An object of mass 12kg is placed on a horizontal, frictionless surface. A force of 36N is exerted on the object for a certain period of time. The velocity of the object becomes 60ms-1 at the end of this time. The force is then removed.

1.1. Calculate the duration for which the force was acting.
1.2. Describe the motion of the object after the force was removed.
The object would continue moving at a constant velocity of 60m.s-1.
All horizontal forces are removed (no friction as well).
According to N(I), as a result of it's inertia, the object must maintain the constant velocity.

2. A 3kg cart moving rightwards, is brought to rest from an initial velocity of 18m.s-1 in 12s by the action of friction between the wheels and the ground.

2.1. Draw the cart and show and label all the forces acting on the cart.
2.2. Calculate the acceleration of the cart.

2.3. Calculate the frictional force.

3. A cyclist is riding a bicycle of 20kg at a constant velocity of 6,4m.s-1. He then applies a constant force of magnitude 80N with the brakes, thus bringing the bicycle to a halt in 4s.

3.1. Calculate the acceleration of the cyclist.

3.2. Calculate the mass of the cyclist.

4. A motorist is traveling in a vehicle of mass 1200kg at a velocity of 118,8km/h. He then notices that he is 85m away from an 80km/h zone. He presses the brake pedal which produces a constant force of magnitude 3600N to the wheels.
Prove that he does not reduce the speed to the required limit.

5. A cart of mass 280kg is pulled by a horse from rest, to a speed of 36km/h in 5s. Calculate the force exerted by the horse if 20% of the applied force was used to overcome friction.

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V. Gokal