Phys 251 Chapter 2

An object moves 20 m east in 30s and then returns to its starting position taking an additional 50 s. If west is chosen as the positive direction, what sign is associated with the average velocity of the object?

- 0 (no sign)

An object moves 20 m east in 30 s and then returns to its starting point taking an additional 50 s. If west is chosen as the positive direction, what is the average speed of the object?

- 0.50 m/s

A baseball is released at rest from the top of the Washington Monument. It hits the ground after falling for 6.0 w. What was the height from which the ball was dropped? ( g= 9.8 m/s² and assume air resistance is negligible)

- 1.8 x 10² m

A vehicle designed to operate on a drag strip accelerates from zero to 30 m/s while undergoing a straight line path of 45 m. What is the vehicle's acceleration if its value may be assumed to be constant?

- 10 m/s²- 240

A cheetah can run at approximately 100 km/hr and a gazette at 80.0 km/hr. If both animals are running at full speed, with the gazelle 70.0 m ahead, how long before the cheetah catches its prey?

- 12.6 s

A rock, released at rest from the top of a tower, hits the ground after 1.5 s. What is the speed of the rock as it hits the ground? (g= 9.8 m/s² and air resistance is negligible)

- 15 m/s

An automobile driver puts on the brakes and decelerates from 30.0 m/s to zero in 10.0 s. What distance does the car travel?

- 150 m

A Cessna aircraft has a lift-off speed of 120 km/hr. What minimum constant acceleration does this require if the aircraft is to be airborne after a take-off run of 240 m?

- 2.31 m/s²

Human reaction time is usually about 0.20 s. If your lab partner holds a ruler between your finger and thumb and releases it without warning, how far can you expect the ruler to fall before you catch it? The nearest value is:

- 20 cm

When a drag strip vehicle reaches a velocity of 60 m/s, it begins a negative acceleration by releasing a drag chute and applying its brakes. While reducing its velocity back to zero, its acceleration along a straight line path is a constant - 7.5 m/s². What displacement does it undergo during this deceleration period?

- 240 m

A rock is thrown straight up with an initial velocity of 24.5 m/s. What maximum height will the rock reach before starting to fall downward? ( Take g equal to 9.80 m/s².)

- 30.6 m

A truck moves 70 m east, then moves 120 m west, and finally moves east again at a distance of 90 m. If east is chosen as the positive direction, what is the truck's resultant displacement?

- 40 m

Omar throws a rock down with speed 12 m/s from the top of a tower. The rock hits the ground after 2.0 s. What is the height of the tower? (air resistance is negligible)

- 44 m

A rock is thrown straight down with an initial velocity of 14.5 m/s from a cliff. What is the rock's displacement after 2.0 s? (Take g equal to 9.80 m/s²)

- 49 m

A basketball player can jump 1.6 m off the hardwood floor. With what upward velocity did he leave the floor?

- 5.6 m/s

A cart is given an initial velocity of 5.0 m/s and experiences a constant acceleration of 2.0 m/s². What is the magnitude of the cart's displacement during the first 6.0 s of its motion?

- 66 m

A drag racer starts from rest and accelerates at 10 m/s² for the entire distance of 400 m (1/4 mile). What is the velocity of the race car at the end of the run?

- 89 m/s

Which of the following is not a vector quantity?

- Temperature

Displacement is which if the following types of quantities?

- Vector

If the displacement of an objects is given in SI units by Δx= -3t + 4t², at t= 2s its velocity and acceleration are, respectively:

- positive, positive

Changing the positive direction in a reference frame to the opposite direction does not change the sign of which of the following quantities?

- speed