Ashley

Ashley 02 Aug 2016 - 3

Question

Which statement about an object moving in a straight line through air is correct?

A When it accelerates, the resultant force acting on it is zero.
B When it moves at a steady speed, the air resistance acting on it is zero.
C When it moves at a steady speed, the resultant force acting on it is zero.
D When it moves, there is a resultant force acting on it.

Answer

According to Newton’s First Law of Motion, when the resultant force is zero, a stationary object remains at rest and a moving object remains moving with constant velocity.

Hence, the answer is C.

Ashley 02 Aug 2016 - 2

Question

The diagram shows a satellite that is moving at a uniform rate in a circular orbit around the Earth.

Which statement describes the motion of this satellite?

A It is accelerating because its speed is changing.
B It is accelerating because its velocity is changing.
C It is not accelerating but its speed is changing.
D It is not accelerating but its velocity is changing.

Answer

As the satellite orbits the Earth, the speed remains the same but the velocity changes.


Since the velocity is changing, there is acceleration.

Answer is B.

Ashley 02 Aug 2016 - 1

Question

A parachutist is falling at terminal velocity, without her parachute open.


She now opens her parachute.

What is the direction of her motion, and what is the direction of her acceleration, immediately after she opens her parachute?

Answer

When the parachutist is falling at terminal velocity, the upwards air resistance is equal to the weight of the parachutist. The resultant force is zero and the velocity is downwards.

When the parachute opens, the air resistance increases and is now greater than the weight.

The resultant force is now upwards and the acceleration is upwards. The velocity is still downwards.

Answer is B.