Question 1

A car is traveling in a straight line with an initial velocity of $$4.0\ \mathrm{m/s} at$$ $$t=0$$ and an acceleration as shown in the graph below. For the first 3 seconds, the acceleration is $$+8\ \mathrm{m/s^2$}$$, and for the next 6 seconds, the acceleration is $$+3\ \mathrm{m/s^2$}. $$What is the car's velocity at $$t=9\ \mathrm{s}$$? (Answer to 2 significant figures.)

Accepted Answer

$$28\ \mathrm{m/s}$$

Question 2

A car starts from rest and accelerates at $$15\ \mathrm{m/s^2$}$$ for $$7\ \mathrm{s}$$, then continues at constant velocity for another $$8\ \mathrm{s}. $$What is the total distance covered by the car in $$15\ \mathrm{s}$$?

Accepted Answer

$$840\ \mathrm{m}$$

Question 3

If two vectors $$\vec{A}$$ and $$\vec{B}$$ satisfy $$\vec{A} + \vec{B} = 0$$, what can you say about their magnitudes and directions?

Accepted Answer

Same magnitude, but must be in opposite directions.

Question 4

A block of mass $$m is $$released from the top of a smooth ramp inclined at an angle $$\alpha. $$What is the acceleration of the block down the ramp?

Accepted Answer

$$g \sin \alpha$$

Question 5

A 10-kg box is at rest on a horizontal surface. The coefficient of static friction is $$0.20. $$What is the minimum force required to start moving the box?

Accepted Answer

$$20\ \mathrm{N}$$

Question 6

A ball is thrown straight up. At the very top of its path, what is the direction of its acceleration vector?

Accepted Answer

Points down.

Question 7

A 50-kg student stands on a scale in an elevator accelerating upward. The scale reads:

Accepted Answer

Greater than $$490\ \mathrm{N}$$

Question 8

A puck is tied to a string and moves in a circle on frictionless ice. If the string breaks, which path does the puck follow?

Accepted Answer

It moves in a straight line tangent to the circle at the point of release.

Question 9

A book rests on a horizontal table. Gravity pulls down on the book. What is the upward force called that the table exerts on the book?

Accepted Answer

Normal force

Question 10

A steel beam hangs from a cable as a crane lifts the beam. What forces act on the beam?

Accepted Answer

Gravity and tension in the cable.

Question 11

A car travels $$30$$ miles south in $$2$$ hours, then $$140$$ miles north in $$3$$ hours. What is the average velocity for the entire trip?

Accepted Answer

$$22\ \mathrm{mph}$$ north

Question 12

A block is pulled to the right over a rough surface. The tension $$T in $$the rope is greater than the kinetic friction $$f_k$$, so the block is speeding up. Suddenly the rope breaks. What happens?

Accepted Answer

The block slows steadily until it stops.

Question 13

A 50-kg astronaut is orbiting the Earth in the space shuttle. Compared to on Earth:

Accepted Answer

His weight is less and his mass is the same.

Question 14

A box is being pulled to the right at steady speed by a rope that angles upward. In this situation, the normal force $$n is$$:

Accepted Answer

$$n \u003c mg$$

Question 15

A mosquito runs head-on into a truck. Which is true during the collision?

Accepted Answer

The mosquito exerts the same force on the truck as the truck exerts on the mosquito.

Question 16

A block of mass $$m is $$suspended from a spring. After being released, while the mass is accelerating downward, the magnitude of the force the mass exerts on the spring is:

Accepted Answer

Smaller than the weight of the mass.

Question 17

A 10 kg box slides horizontally without friction at a speed of 1 m/s. A constant force is applied in the direction of motion for 5 m, after which the box's speed is 2 m/s. What is the magnitude of the applied force?

Accepted Answer

$$3\ \mathrm{N}$$

Question 18

A ball rolls down an incline and off a horizontal ramp. Ignoring air resistance, what force(s) act on the ball as it moves through the air just after leaving the ramp?

Accepted Answer

The weight of the ball acting vertically down.

Question 19

A ring is pulled on by three forces and is not moving. Two of the forces are $$10\ \mathrm{N} at an $$angle $$	heta$$ above the horizontal on each side. What is the magnitude of the third force $$F$$ required to keep the ring at rest?

Accepted Answer

$$20\sin	heta\ \mathrm{N}$$

Interpreting Piecewise Acceleration in 1D Kinematics

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