## Tuesday, October 13, 2009

### Sneak peak at tomorrows test

A 2.0-kilogram laboratory cart is sliding across a horizontal frictionless surface at a constant velocity of 4.0 meters per second east. What will be the cart’s velocity after a 6.0-newton westward force acts on it for 2.0 seconds?

(1) 2.0 m/s east (3) 10. m/s east (2) 2.0 m/s west (4) 10. m/s west

Base your answers to questions 2 and 3 on the diagram below, which shows a 1.0- newton metal disk resting on an index card that is balanced on top of a glass.

What is the net force acting on the disk?

(1) 1.0 N (3) 0 N (2) 2.0 N (4) 9.8 N

When the index card is quickly pulled away from the glass in a horizontal direction, the disk falls straight down into the glass. This action is a result of the disk’s

(1) inertia (3) shape (2) charge (4) temperature

Compared to the force needed to start sliding a crate across a rough level floor, the force needed to keep it sliding once it is moving is

(1) less (2) greater (3) the same

A 400-newton girl standing on a dock exerts a force of 100 newtons on a 10 000-newton sailboat as she pushes it away from the dock. How much force does the sailboat exert on the girl?

(1) 25 N (3) 400 N (2) 100 N (4) 10 000 N

Which vector diagram best represents a cart slowing down as it travels to the right on a horizontal surface?

Equilibrium exists in a system where three forces are acting concurrently on an object. If the system includes a 5.0-newton force due north and a 2.0-newton force due south, the third force must be

(1) 7.0 N south (3) 3.0 N south (2) 7.0 N north (4) 3.0 N north

Two forces are applied to a 2.0-kilogram block on a frictionless horizontal surface, as shown in the diagram below.

The acceleration of the block is

(1) 1.5 m/s2 to the right (2) 2.5 m/s2 to the left (3) 2.5 m/s2 to the right

(4) 4.0 m/s2 to the left

A student applies a 20.-newton horizontal force to move a 30.0 newton crate at a constant speed of 4.0 meters per second across a rough floor. What is the value of ยต

(1) 1.0 (3) .666 (2) .200 (4) .133

The diagram below shows a block on a horizontal frictionless surface. A 100.-newton force acts on the block at an angle of 30.° above the horizontal.

What is the magnitude of force F if it establishes equilibrium?

(1) 50.0 N (3) 100. N (2) 86.6 N (4) 187 N

The graph below represents the relationship between the forces applied to an object and the

corresponding accelerations produced.

What is the inertial mass of the object?

(1) 1.0 kg (3) 0.50 kg (2) 2.0 kg (4) 1.5 kg

The diagram below shows a sled and rider sliding down a snow-covered hill that makes an angle of 30.° with the horizontal.

Which vector best represents the direction of the normal force, FN, exerted by the hill

The diagram below represents a block sliding down an incline.

Which vector best represents the frictional force acting on the block?

(1) A (3) C (2) B (4) D

A 50.-newton horizontal force is needed to keep an object weighing 500. newtons moving at a constant velocity of 2.0 meters per second across a horizontal surface. The magnitude of the frictional force acting on the object is

(1) 500. N (3) 50. N (2) 450. N (4) 0 N

A series of unbalanced forces was applied to each of two blocks, A and B. The graphs below show the relationship between unbalanced force and acceleration for each block.

Compared to the mass of block A, the mass of block B is

(1) the same (3) half as great (2) twice as great (4) four times as great

A different force is applied to each of four 1-kilogram blocks to slide them across a uniform steel surface at constant speed as shown below. In which diagram is the coefficient of friction between the block and steel smallest?

Which two graphs represent the motion of an object on which the net force is zero?

The coefficient of kinetic friction between a 780.-newton crate and a level warehouse floor is

0.200. Calculate the magnitude of the horizontal force required to move the crate across the floor at constant speed. [Show all work, including the equation and substitution with units.]

The sign below hangs outside the physics classroom, advertising the most important truth to be found inside. The sign is supported by a diagonal cable and a rigid horizontal bar. If the sign has a mass of 50 kg, then determine the tension in the diagonal cable which supports its weight.

A 20 kg weight that is on a ledge is attached with a string, to another 20 kg weight that is hanging over the edge of the perfectly flat ledge. Assuming that the coefficient of friction is 0.2, what is the acceleration and what is the tension in the string? (show all work)

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