Physics - Study Mode

[#271] A boy sitting in a train moving with a uniform velocity drops a coin outside. A man standing outside the train will find the trajectory of the coin to be
Correct Answer

(A) A parabola

Explanation

Solution: Parabola, because when the coin is dropped at a particular point, it has the same velocity as the running train. So, by Newton's first law, it continues its motion horizontally with that velocity. But then, it is also pulled down by earth's gravity continuously. In this situation its horizontal motion gives way to the parabolic motion until it reaches the ground.

[#272] During uniform motion of an object along a straight line, its ________ remains constant with time.
Correct Answer

(D) Velocity

Explanation

Solution: During uniform motion of an object along a straight line, its velocity remains constant with time.

[#273] Find the acceleration (in m/s 2 ) of a body which accelerates from 25 m/s to 30 m/s in 10 seconds
Correct Answer

(D) 0.5

Explanation

Solution: u(initial velocity) = 25m/s v(final velocity) = 30m/s t(time) = 10s a = (v-u)/t a = (30-25)/10 a = 5/10 a = 1/2 a = 0.5m/s²

[#274] Acceleration is
Correct Answer

(D) Directly proportional to force

Explanation

Solution: Acceleration is directly proportional to force.

[#275] A tennis ball machine serves a ball vertically into the air from a height of 2 feet, with an initial speed of 110 feet per second. After how many seconds does the ball attain its maximum height?
Correct Answer

(B) 3.44 sec

Explanation

Solution: It is launched vertically with an initial speed of 110 ft/sec. It will reach maximum height when the speed drops to 0. Vo = 110 feet per second ho = 2 feet So, h(t) = -16t^2 +110t +2 Take the derivative: h'(t) = 110 -32t The maximum height will be at the inflection when the derivative crosses the x-axis, then h'(t)=0. So, set h'(t)=0 and solve for t: 0 = 110 -32t -110 = -32t t = 3.4375 t = 3.44 seconds.