Newton's Laws and Dynamics Questions

A skydiver of mass 80 kg falls vertically with a constant speed of 50 m s^–1. The upward force acting on the skydiver is approximately

• 0 N.

• 80 N.

• 800 N.

• 4000 N.

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A car of mass 1000 kg accelerates on a straight, flat, horizontal road with an acceleration

a = 0.3 m s^–2.

The driving force F on the car is opposed by a resistive force of 500 N.

The net (resultant) force on the car is

• 200 N.

• 300 N.

• 500 N.

• 800 N.

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A wooden block is sliding down an inclined plane at constant speed. The magnitude of the frictional force between the block and the plane is equal to

• zero.

• the magnitude of the weight of the block.

• the magnitude of the component of weight of the block parallel to the plane.

• the magnitude of the component of the normal reaction parallel to the plane.

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Stephen pushes two boxes P and Q, that stay in contact, along a rough table, with a force F of 30 N.

Box P has a mass of 2.0 kg and box Q has a mass of 4.0 kg. Both boxes move with constant speed.

The resultant force on box Q is

• 0 N.

• 5.0 N.

• 15 N.

• 30 N.

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A cart of mass M is on a horizontal frictionless table.

The cart is connected to an object of weight W via a pulley. Which of the following is the acceleration of the cart?

• 
• 
• 
• 0

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Two steel balls, of mass M and 2M, fall at constant speeds in a tube filled with oil.

Which of the following correctly compares the magnitudes of the net force and of the drag (resistance) force on the two balls?

• A

• B

• C

• D

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A skydiver jumped out of an airplane. On reaching a terminal speed of 60 m s^–1, she opened her parachute. Which of the following describes her motion after opening her parachute?

• She went upwards for a short time, before falling to Earth at a speed of 60 m s^–1.

• She continued downwards at 60 m s^–1, but hit the ground with less force.

• She continued to fall but reached a new terminal speed of less than 60 m s^–1.

• She went upwards for a short time, before falling to Earth at a speed of less than 60 m s^–1.

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The diagram shows a girl attempting (but failing) to lift a heavy suitcase of weight W. The magnitude of the vertical upwards pull of the girl on the suitcase is P and the magnitude of the vertical reaction of the floor on the suitcase is R.

Which equation correctly relates W, P and R?

• W = P + R

• W > P + R

• W < P + R

• W = P = R

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Objects A and B collide together. They end up joined together and stationary. During the collision, a force +F is exerted on object A by object B. According to Newton’s third law, there will also be a force of

• –F acting on object B.

• –F acting on object A.

• +F acting on object B.

• +F acting on object A.

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A student is sitting on a chair. One force that is acting on the student is the pull of gravity. According to Newton’s third law, there must be another force which is

• the upward push of the chair on the student.

• the downward force on the student.

• the downward push of the chair on Earth.

• the upward force on Earth.