1. Two objects of the same mass fall from different heights. If air friction is
ID: 306440 • Letter: 1
Question
1. Two objects of the same mass fall from different heights. If air friction is negligible then they will land on the ground (A) at the same time but different speeds and accelerations (B) at the same time and speed but different accelerations (C) all values will be the same (D) at different speeds, times but the same acceleration 2. A projectile of mass mi is launched horizontally from a height of 100 m and speed 10 m s1. Another projectile of mass m2 free falls from the same height. The experiment is taking place on Mars, where the gravity is about 1/2 of that of Earth. Atmospheric resistance can be neglected. The two projectiles will land on the ground (A) at the same time (B) at different times (C) can be either or, depending on their masses 3. A projectile has a velocity of (3t)i- (t2) j, where t is time in seconds. At t-2 s, its acceleration magnitude will be (A) 5ms2 (B) 6 m s2 (C) 7 m s2 (D) cannot be determined 4. The expression uot +1/2 a-t, where is uo speed, t is time and a is acceleration represents (A) speed (B) distance (C) acceleration (D) none of the above 5. The graph between time (x-axis) and distance (y-axis) for a projectile that moves at a constant positive acceleration will be a (A) straight line (B) a line curved upward (C) a line curved downward (D) none of the above 6. If you apply Newton's law on two objects of different masses that are free falling from different height with no air resistance then you will conclude that both objects accelerate (A) proportional to their masses ratio (B) reversely proportional to their masses ratio (C) none of these 7. A force equal to 1000 N acts on a 100 kg mass on a frictionless horizontal surface. The object starts from rest. How fast is it going after 2s? (A) 5 ms-1 (B) 10 ms-1 (C) 15 ms-1 (D) 20 ms-1 (E) 25 ms-1 8. A force equal to 500 N is required to barely move a 100 kg mass on a horizontal surface. Find the static friction coefficient between the objectExplanation / Answer
1. acceleration of free fall is 9.80 m/s^2 downwards always.
and height is different so time and speed will be different as they depends upon height from dropped.
(independent of mass)
Ans: (D)
2. case1: initial vertical velocity, v0y = 0
ay = - g_mars
d = yf - yi = 0 - h = - h
case2: initial vertical velocity, v0y = 0
ay = - g_mars
d = yf - yi = 0 - h = - h
and d = v0y t + ay t^2 /2
every quantity is same for both so t will also be same.
Ans: (A) at the same time
3. v = 3ti - t^2 j
a = dv/dt = 3 i - 2t j
t = 2 s
a = 3i - 4 j
magnitude = sqrt(3^2 + (-4)^2) = 5 m/s^2
Ans(A)
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