Physics 201, Midterm Exam 2Oct. 26, 1999

1.

A cat jumps up vertically, leaving the ground with a speed of 8 m/s. What height will it reach?

a) need to know the mass of the cat
b) 1.6 m
c) 2.4 m
*d) 3.2 m
e) 5.8 m

2.

A 0.1 kg stone held by a 1m string is rotated faster and faster on a horizontal circle, until the string breaks when the angular velocity exceeds 100. rad/s. What is the mass of the heaviest weight that you could hang from the string before it breaks?

a) 0.1 kg
b) 1 kg
c) 10 kg
*d) 100 kg
e) 1000 kg

3.

If you climb to the top of Mt. Everest, which of the following statements is not true ?

a) your total mechanical energy has increased
*b) gravity has done positive work on you
c) your gravitational potential energy has increased
d) if you moved with constant velocity, no net work was done
e) if you had been lighter, your muscles would have done less work

4.

The two rams of test 1 are still fighting, but in their last collision they get their horns locked. Just before the collision, the big 120 kg ram was moving at 4 m/s East, while the smaller 80 kg one was moving at 5 m/s West. In which direction and with what speed will they move when they get stuck together?

*a) 0.4 m/s East
b) 4.4 m/s East
c) 4.4 m/s West
d) 2.2 m/s West
e) 0.4 m/s West

5.

If a car drives up a hill with constant positive acceleration

a) total mechanical energy is conserved
b) the increase in kinetic energy is compensated by a decrease in potential energy
c) kinetic and potential energy increase at the same rate
d) the increase in potential energy is compensated by a decrease in kinetic energy
*e) none of the above

6.

While going around a bend, a car experiences a centripetal acceleration of 24 m/s². What would the acceleration be if it went at twice the speed around a bend of twice the radius?

a) 6 m/s²
b) 12 m/s²
c) 24 m/s²
*d) 48 m/s²
e) 96 m/s²

7.

(Note: wording modified the way I had meant it to be)
A bomb initially at rest explodes into three pieces. Two of the pieces have the same mass, and they fly apart in equal and opposite velocities. What will the third piece do?

a) not enough information
b) there is no solution compatible with momentum conservation
*c) the third piece will be at rest
d) the third piece will fly perpendicularly to the direction of the other two, with undetermined velocity
e) the third piece will fly parallel to the direction of the other two, with undetermind velocity

8.

A strong wind coming from the South East exerts a force on two airplanes moving with constant velocity, one directed due East and the other due North. The work done by the wind

a) is zero in either case, since the planes have constant velocity
b) is positive for both planes
c) is negative for both planes
d) is positive for the eastbound plane, negative for the northbound
*e) is positive for the northbound plane, negative for the eastbound

9.

When an object is in uniform circular motion

a) velocity and acceleration point in the same direction
b) velocity and acceleration are not in a fixed relation, since the velocity's direction changes all the time while the acceleration is always the same
c) velocity and acceleration point in opposite directions
*d) velocity and acceleration are perpendicular to each other
e) none of the above statements applies to uniform circular motion

10.

You stand at one end of a light (a few kilos) wheel-mounted cart, and start walking towards the other end. The cart will

a) remain still
b) move opposite to your direction, at the same speed as you
c) move opposite to your direction, but at a lower speed
*d) move opposite to your direction, but at a higher speed
e) none of the above

11.

At what latitude does the earth have the greatest angular velocity?

a) 0⁰ (i.e. at the equator)
b) 30⁰
c) 45⁰
d) 60⁰
*e) none of these

12.

Walking at a steady pace, a 70 kg hiker follows an uphill trail with an 11.5⁰ slope. If in 1 hour he covers 2.5 km, what is his average power output ?

*a) 0.1 kW
b) 0.1 kWh
c) 0.5 kW
d) 0.5 kWh
e) 0.01 kW

13.

A 900 kg car screeches to a halt, leaving a 15 m long skid mark. If it is known that the average frictional force exerted by the ground on the tires is 27 kN, how fast was the car going ?

a) not enough information
b) 15 m/s
*c) 30 m/s
d) 45 m/s
e) 60 m/s

14.

A model airplane attached to a 2 m guide wire is flying in a circle. At one instant, its velocity is 20 m/s and its acceleration vector makes an angle of 60⁰ with the wire. What is the magnitude of the tangential acceleration?

a) 0 m/s²
b) 200 m/s²
c) 115.5 m/s²
*d) 346.4 m/s²
e) not enough information

15.

A beetle is walking at constant speed along a radius of a turntable that is rotating at a constant 33 rpm rate. Which of the following statements is not correct about the beetle:

a) with respect to the turntable, it has constant velocity
b) with respect to the ground, it has constant angular velocity
c) with respect to the ground, it has variable tangential velocity
d) with respect to the ground, it has zero angular acceleration
*e) all statements are correct

16.

An apple is tossed up in the air and eventually falls to the ground while another one is allowed to fall to the ground starting from the same height. Ignoring air resistance, the total work done on the apples after they leave the hand

a) is zero, since there are no force involved
b) is larger for the apple tossed up in the air
c) is negative for both apples
*d) is the same for both apples
e) is more negative for the apple tossed up in the air

17.

Which of the following statement is true?

a) if two objects have the same momentum, they have the same kinetic energy
b) if two objects have the same mass and speed, they have the same momentum
*c) if two object have the same mass and speed, they have the same kinetic energy
d) if two objects have the same kinetic energy, they have the same momentum
e) all the above statements are true

18.

In the largest existing particle accelerators, located in an underground circular tunnel 31.4 km long straddling the Swiss- French border, electrons are moving at practically the speed of light ( 3x10⁸ m/s). To keep an electron on its orbit requires a (magnetic) force of 16.4x10^-18 N. What is the mass of the electron?

*a) 9.1x10^-31 kg
b) 5.72x10^-30 kg
c) 5.1x10^-17 kg
d) 9.1x10^-34 kg
e) 5.72x10^-33kg

19.

A coin is positioned on a perfectly frictionless turntable, when the turntable start rotating with constant angular acceleration $\alpha$. When this happens, the coin

*a) will remain still
b) will be thrown off the turntable along the direction of the tangent
c) will start moving with angular acceleration $\alpha$
d) will start moving someway, but one cannot say how
e) none of the above

20.

A skater of mass M gliding along the ice at velocity v, picks up a glove of mass m from the ground. After this happens, his velocity is

a) v
b) (M+m)v
c) (M-m)v
*d) Mv/(M+m)
e) none of the above

21.

A skater of mass M gliding along the ice at velocity v, drops a glove of mass m. After this happens, his velocity is

*a) v
b) v(M-m)/M
c) Mv/(M-m)
d) (M-m)v
e) none of the above

22.

As a 0.2 kg frog leaps at a forward angle, the components of its initial velocity are 2 m/s horizontally and 3 m/s vertically. What is its kinetic energy at the highest point of its trajectory ?

a) 0. J
*b) 0.4 J
c) 0.9 J
d) 1.3 J
e) 2.5 J

23.

In a penalty kick, a 500 g soccer ball acquires a speed of 30 m/s. If the average force applied to the ball is 3kN, for how long was the foot in contact with the ball?

a) Not enough information
b) 3 ms
*c) 5 ms
d) 0.03 s
e) 0.015 s

24.

A spinning wheel initially moving at 20 rad/s comes to a stop in 40 seconds. What is the magnitude of the average angular acceleration?

a) 2 rad/s²
*b) 0.5 rad/s²
c) 2 $\pi$ rad/s²
d) $\pi$/2 rad/s²
e) none of the above

25.

By choosing the correct combination of speed, radius of curvature and banking angle, a car can go around a bend without sliding even if the surface is perfectly frictionless. Suppose now that the same car moves with the same speed on a curve with the same banking angle, but on the moon rather than on the earth. In this case the no-slipping radius will be

a) the same as on earth
*b) larger than on earth
c) smaller than on earth
d) the answer will depend on the mass of the car
e) need to know the actual values of velocity and banking angle to answer