CBA 2 Review - 8th Grade Science

A student pushes a 51.5 kg bookshelf across a smooth floor with a net force of 67 N. What is the approximate acceleration of the bookshelf?

• 1.3 m/s2

• 3,450.5 m/s2

• 15.5 m/s2

• 0.77 m/s2

Answer explanation

A = F/M, so you have to divided the force (67 N) by the mass (51.5 kg) to get the right answer.

Tags

NGSS.MS-PS2-2

A toy truck is at rest on the floor. Which statement describes to=he forces acting on the toy truck?

• The forces are balanced so motion occurs

• The forces are balanced so no motion occurs

• The forces are unbalanced so motion occurs

• The forces are unbalanced so no motion occurs

Answer explanation

Balanced force means that there is no motion; the forces on the truck are balanced, so no motion occurs.

The net force on a vehicle that is accelerating at a rate of 1.5 m/s2 is 1,800 Newtons. What is the mass of the vehicle to the nearest kg?

• 5

• 12

• 1200

• 130000

Answer explanation

M = F/A. To get the correct answer, you have to divide 1,800 N by 1.5 m/s2.

Tags

NGSS.MS-PS2-2

a 1,100 kg car comes uniformly to a stop. If the vehicle is accelerating at -1.2 m/s2, which force is closest to the net force acting on the vehicle?

• -9,600 N

• -1,300 N

• -900 N

• -94 N

Answer explanation

F = M x A. To find the correct answer, you need to multiply 1,100 kg by -1.2 m/s2, then choose the CLOSEST answer.

Tags

NGSS.MS-PS2-2

A large rock is motionless on a flat sidewalk. Which statement best explains why the rock remains motionless?

• There are no forces acting on the rock

• The only force acting on the rock is directed toward the sidewalk

• The forces acting on the rock are all balanced

• The sidewalk exerts an unbalanced force on the rock

Answer explanation

Balanced force means there is no motion; for the rock to remain motionless, the forces have to be balanced.

A pitcher throws a ball toward a player holding a softball bat. The player uses the bat to hit the ball. The bat applies a 10-newton force to the ball. Which statement correctly describes the reaction force between the bat and ball?

• The reaction force is the force that causes the ball to move toward the bat.

• The reaction force is the force applied to the bat by the player holding the bat

• The reaction force is the force that pulls the bat toward the ground

• The reaction force is the force of the ball on the bat.

Answer explanation

The ACTION is any work done by a body or object; the REACTION force is the result of that work. A ball player hitting the ball is the work, and the result is the ball hitting the bat and flying away.

Tags

NGSS.MS-PS2-1