Forces and Newton's Laws

Two people each have a mass of 75 kg. They are both in an elevator that has a mass of 350kg. When the elevator begins to move, the people and the elevator have an upward

acceleration of 2.00 m/s2. What is the net force that acts on the elevator as it accelerates upward ?

• 9.8N

• 150N

• 500N

• 1000N

Answer explanation

A net force acting on a 5.8 kg box produces an acceleration of 3.2 m/s2.

What acceleration, to the NEAREST TENTH of a m/s2, will the same net force cause on a 3.0 kg box?

Answer explanation

The picture shows an apple with a mass of 1.3 kg falling from a 15.0 m high tree.

Earth’s gravity is acting on the apple. Which statement best describes the reaction force to

Earth’s gravity in this situation?

• The apple is pulling on Earth with a force of 12.74 N.

• The sun is pulling on Earth with a force of 5.97 N.

• Earth is pulling on the ground with a force of 25 N.

• Earth is pulling on the air with a force of 2.28 N.

The girl applies a horizontal force of 47 N on the cart that has a mass of 52 kg, as shown. The magnitude of the normal force acting on the cart is

• 52N

• 0N

• 509.6N

• 2444N

Answer explanation

What is inertia?

• push or pull on an object

• the natural tendency of an object to

  remain at rest or in motion at a constant speed along a straight line

• rate of change in speed or direction

• acceleration due to gravity

A lab cart is loaded with different masses and moved at various velocities. Which diagram

shows the cart-mass systems with the greatest inertia?

• 1

• 2

• 3

• 4

Answer explanation

more mass, greater inertia

slower acceleration

What is the minimum force required to accelerate a 10 kg rectangular box at a rate of 2.7m/s2 ?

• 27N

• 270N

• 3.7N

• 370N

Inertia is most closely related to

• weight

• force

• gravity

• mass

Kim (50 kg) and Jay (75kg) stand motionless on ice skates facing each other at arm's length on a smooth frozen pond. Which of the following actions will give Jay the greatest speed?

HINT: a = f/m and v = a*t

• Jay pushes Kim with a 100 N force for 0.58 seconds.

• Kim pushes Jay with a force of 80 N for 0.3 seconds.

  .

• .

  Jay pushes Kim with a 100 N force for 0.3 seconds.

• Kim pushes Jay with a force of 350 N for 0.04 seconds.

The figure shows a 10Kg block that is being pulled along the floor with a force of 20N. According to the figure, what is the acceleration of the block?

(Express your answer to the nearest whole number, in m/s2)

• 1 m/s2

• 2 m/s2

• 3 m/s2

• 4 m/s2

Answer explanation

a= F/m