Unit 8.3 Answers to Questions 1 to 9

1    Newton’s first law of motion states that:

•      an object at rest will remain this way unless it is acted upon by a force

•      an object that is moving will continue to move at the same speed and in the same direction unless a force acts upon it.

2    a  Newton’s second law of motion:

Fnet = m × a where Fnet is the total force acting on an object measured in newtons (N), m is the mass of the object (kg) and a is the acceleration of the object (m/s2).

b  a = Fnet/m

3    Voyager 1 is still in motion because no force has acted upon it to stop its motion.

4    If a car collides with a stationary object, such as a pole, the occupants of the car continue to travel forward with the speed that they had before the impact. This means that if the driver or a passenger is forced against a sharp object, such as a radio dial in the front of the car, this could cause damage in an accident. Similarly, loose objects in the back of the car will continue to travel forward in such an accident and can hit an occupant in the front of the car.

5    The car will only accelerate, i.e. increase or decrease speed, if unbalanced forces are acting upon it. If the forces on the car are balanced, then its acceleration is zero; the car may be travelling at a constant speed, in which case its acceleration is zero.

6    An airfoil describes the cross-sectional shape of an aircraft wing. The base of the wing is flat and the top surface is curved. Air flows more rapidly over this top curved surface, which creates a lift force.

7    The racquet applies an action force to the tennis ball upon impact. The ball applies an equal and opposite reaction force back on the racquet.

8    Objects with more mass possess greater inertia. Therefore, the suitcase packed for a holiday has greater inertia than the same suitcase when it is emptied.

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