# Homework Help: Physics mechanics questions

1. Jan 26, 2010

### key

Hi can i please get some help with these questions

1.A sphere of mass M, radius r, and rotational inertia I is released from rest at the top of an inclined plane of height h

If the plane is frictionless, what is the speed vcm, of the center of mass of the sphere at the bottom of the incline?
(A) Square root of 2gh (B) 2Mgh/I (C) 2Mgh(r)squared/I (D) Square root of answer C

I think it is A

2. The momentum p of a moving object as a function of time t is given by the expression p = kt3, where k is a constant. The force causing this motion is given by the expression
(A) 3kt2 (B) 3kt2/2 (C) kt2/3 (D) kt4 (E) kt4/4

I think the answer is E

3. A mass M suspended by a spring with force constant k has a period T when set into oscillation on Earth. Its period on Mars, whose mass is about 1/9 and radius 1/2 that of Earth, is most nearly
(A) 1/3 T (B) 2/3 T (C) T (D) 3/2 T (E) 3 T

I think the answer is C

4. A student is testing the kinematic equations for uniformly accelerated motion by measuring the time it takes for light weight plastic balls to fall to the floor from a height of 3 m in the lab. The student predicts the time to fall using g as 9.80 m/s2 but finds the measured time to be 35% greater. Which of the following is the most likely cause of the large percent error?
(A) The acceleration due to gravity is 70% greater than 9.80 m/s2 at this location.
(B) The acceleration due to gravity is 70% less than 9.80 m/s2 at this location.
(C) Air resistance increases the downward acceleration.
(D) The acceleration of the plastic balls is not uniform.
(E) The plastic balls are not truly spherical.

I think the answer is A

5. An object is thrown with velocity v from the edge of a cliff above level ground. Neglect air resistance. In order for the object to travel a maximum horizontal distance from the cliff before hitting the ground, the throw should be at an angle θ with respect to the horizontal of
(A) greater than 60° above the horizontal
(B) greater than 45° but less than 60° above the horizontal
(C) greater than zero but less than 45° above the horizontal
(D) zero
(E) greater than zero but less than 45° below the horizontal

I think the answer is D

6. The escape speed for a rocket at Earth's surface is ve . What would be the rocket's escape speed from the surface of a planet with twice Earth's mass and the same radius as Earth?
(A) 2 ve (B) (C) ve (D) (E) ve/2

I think the answer is A

7. A 1.0 kg mass is attached to the end of a vertical ideal spring with a force constant of 400 N/m. The mass is set in simple harmonic motion with an amplitude of 10 cm. The speed of the 1.0 kg mass at the equilibrium position is
(A) 2 m/s (B) 4 m/s (C) 20 m/s (D) 40 m/s (E) 200 m/s

I think the answer is C

thank you so much for the help

2. Jan 26, 2010

### Redbelly98

Staff Emeritus

3. Jan 26, 2010

### key

could you please tell me the ones i got wrong i will show you my work for those
thanks

Last edited: Jan 26, 2010
4. Jan 27, 2010

### Redbelly98

Staff Emeritus
I checked the first 4 questions; #2 and #4 are wrong.

I don't have time to work out all 7 questions, in the future I suggest posting questions separately.